[BUG] crash on make test

I got a crash on git's make test with and a core file in ./t/trash directory.t4200-rerere/
The problem seems to be in garbage_collect (builtin-rerere.c) where readdir can be called with a null pointer

Below is the gdb stack trace:

GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu"...
Reading symbols from /lib/libz.so.1...done.
Loaded symbols for /lib/libz.so.1
Reading symbols from /lib/i686/cmov/libcrypto.so.0.9.8...done.
Loaded symbols for /lib/i686/cmov/libcrypto.so.0.9.8
Reading symbols from /lib/tls/i686/cmov/libpthread.so.0...Reading symbols from /usr/lib/debug/lib/tls/i686/cmov/libpthread-2.9.so...done.
done.
Loaded symbols for /lib/tls/i686/cmov/libpthread.so.0
Reading symbols from /lib/tls/i686/cmov/libc.so.6...Reading symbols from /usr/lib/debug/lib/tls/i686/cmov/libc-2.9.so...done.
done.
Loaded symbols for /lib/tls/i686/cmov/libc.so.6
Reading symbols from /usr/lib/libxml2.so.2...done.
Loaded symbols for /usr/lib/libxml2.so.2
Reading symbols from /lib/tls/i686/cmov/librt.so.1...Reading symbols from /usr/lib/debug/lib/tls/i686/cmov/librt-2.9.so...done.
done.
Loaded symbols for /lib/tls/i686/cmov/librt.so.1
Reading symbols from /lib/tls/i686/cmov/libdl.so.2...Reading symbols from /usr/lib/debug/lib/tls/i686/cmov/libdl-2.9.so...done.
done.
Loaded symbols for /lib/tls/i686/cmov/libdl.so.2
Reading symbols from /usr/lib/libelf.so.1...done.
Loaded symbols for /usr/lib/libelf.so.1
Reading symbols from /usr/lib/libstdc++.so.6...done.
Loaded symbols for /usr/lib/libstdc++.so.6
Reading symbols from /lib/tls/i686/cmov/libm.so.6...Reading symbols from /usr/lib/debug/lib/tls/i686/cmov/libm-2.9.so...done.
done.
Loaded symbols for /lib/tls/i686/cmov/libm.so.6
Reading symbols from /lib/libgcc_s.so.1...done.
Loaded symbols for /lib/libgcc_s.so.1
Reading symbols from /lib/ld-linux.so.2...Reading symbols from /usr/lib/debug/lib/ld-2.9.so...done.
done.
Loaded symbols for /lib/ld-linux.so.2
Core was generated by `git rerere gc'.
Program terminated with signal 11, Segmentation fault.
[New process 5637]
#0  0x4027fca5 in __readdir64 (dirp=0x0) at ../sysdeps/unix/readdir.c:45
 in ../sysdeps/unix/readdir.c
(gdb) bt full
#0  0x4027fca5 in __readdir64 (dirp=0x0) at ../sysdeps/unix/readdir.c:45
 ignore1 = 0
 ignore2 = 1
 dp = <value optimized out>
 saved_errno = 12
#1  0x0813cfd4 in garbage_collect (rr=0xbfabe89c) at builtin-rerere.c:51
 to_remove = {items = 0x0, nr = 0, alloc = 0, strdup_strings = 1}
 dir = (DIR *) 0x0
 e = (struct dirent *) 0x1
 i = 0
 cutoff = -1079252800
 now = 1259852637
 then = 1
#2  0x0813d970 in cmd_rerere (argc=2, argv=0xbfabeaa8, prefix=0x0) at builtin-rerere.c:121
 merge_rr = {items = 0xa0d2728, nr = 1, alloc = 32, strdup_strings = 1}
 i = -1
 fd = 6
#3  0x0804ca57 in run_builtin (p=0x831465c, argc=2, argv=0xbfabeaa8) at git.c:249
 status = 1076211824
 st = {st_dev = 3418922014550254984, __pad1 = 65535, __st_ino = 1073860596, st_mode = 134517300, 
  st_nlink = 1073862256, st_uid = 3215714640, st_gid = 1073798779, st_rdev = 4632177755147065384, __pad2 = 1, 
  st_size = 1, st_blksize = 134519071, st_blocks = 180, st_atim = {tv_sec = 137446088, tv_nsec = 1}, st_mtim = {
    tv_sec = 1075774256, tv_nsec = 1077161972}, st_ctim = {tv_sec = 137183648, tv_nsec = 134524528}, 
  st_ino = 4612030924696840600}
 prefix = 0x0
#4  0x0804cee8 in handle_internal_command (argc=2, argv=0xbfabeaa8) at git.c:394
 p = (struct cmd_struct *) 0x831465c
 cmd = 0xbfac098a "rerere"
 i = 69
 commands = {{cmd = 0x82d4765 "add", fn = 0x804f757 <cmd_add>, option = 5}, {cmd = 0x82d4769 "stage", 
    fn = 0x804f757 <cmd_add>, option = 5}, {cmd = 0x82d476f "annotate", fn = 0x8050754 <cmd_annotate>, option = 1}, {
    cmd = 0x82d4778 "apply", fn = 0x80679e1 <cmd_apply>, option = 0}, {cmd = 0x82d477e "archive", 
    fn = 0x8069ba0 <cmd_archive>, option = 0}, {cmd = 0x82d4786 "bisect--helper", 
    fn = 0x806a138 <cmd_bisect__helper>, option = 5}, {cmd = 0x82d4795 "blame", fn = 0x807770d <cmd_blame>, 
    option = 1}, {cmd = 0x82d479b "branch", fn = 0x807d584 <cmd_branch>, option = 1}, {cmd = 0x82d47a2 "bundle", 
    fn = 0x807e3ec <cmd_bundle>, option = 0}, {cmd = 0x82d47a9 "cat-file", fn = 0x80803cb <cmd_cat_file>, 
    option = 1}, {cmd = 0x82d47b2 "checkout", fn = 0x8088f1c <cmd_checkout>, option = 5}, {
    cmd = 0x82d47bb "checkout-index", fn = 0x8082fc9 <cmd_checkout_index>, option = 5}, {
    cmd = 0x82d47ca "check-ref-format", fn = 0x8081920 <cmd_check_ref_format>, option = 0}, {
    cmd = 0x82d47db "check-attr", fn = 0x808125a <cmd_check_attr>, option = 1}, {cmd = 0x82d47e6 "cherry", 
    fn = 0x80eb740 <cmd_cherry>, option = 1}, {cmd = 0x82d47ed "cherry-pick", fn = 0x814c341 <cmd_cherry_pick>, 
    option = 5}, {cmd = 0x82d47f9 "clone", fn = 0x808e8a1 <cmd_clone>, option = 0}, {cmd = 0x82d47ff "clean", 
    fn = 0x808aa34 <cmd_clean>, option = 5}, {cmd = 0x82d4805 "commit", fn = 0x809b274 <cmd_commit>, option = 5}, {
    cmd = 0x82d480c "commit-tree", fn = 0x8092531 <cmd_commit_tree>, option = 1}, {cmd = 0x82d4818 "config", 
    fn = 0x809f881 <cmd_config>, option = 0}, {cmd = 0x82d481f "count-objects", fn = 0x80a1c75 <cmd_count_objects>, 
    option = 1}, {cmd = 0x82d482d "describe", fn = 0x80a4d6d <cmd_describe>, option = 1}, {cmd = 0x82d4836 "diff", 
    fn = 0x80a99e8 <cmd_diff>, option = 0}, {cmd = 0x82d483b "diff-files", fn = 0x80a56d0 <cmd_diff_files>, 
    option = 5}, {cmd = 0x82d4846 "diff-index", fn = 0x80a601c <cmd_diff_index>, option = 1}, {
    cmd = 0x82d4851 "diff-tree", fn = 0x80a7307 <cmd_diff_tree>, option = 1}, {cmd = 0x82d485b "fast-export", 
    fn = 0x80af36f <cmd_fast_export>, option = 1}, {cmd = 0x82d4867 "fetch", fn = 0x80c1668 <cmd_fetch>, 
    option = 1}, {cmd = 0x82d486d "fetch-pack", fn = 0x80ba759 <cmd_fetch_pack>, option = 1}, {
    cmd = 0x82d4878 "fetch--tool", fn = 0x80b4202 <cmd_fetch__tool>, option = 1}, {cmd = 0x82d4884 "fmt-merge-msg", 
    fn = 0x80c5038 <cmd_fmt_merge_msg>, option = 1}, {cmd = 0x82d4892 "for-each-ref", 
    fn = 0x80cb172 <cmd_for_each_ref>, option = 1}, {cmd = 0x82d489f "format-patch", 
    fn = 0x80e86a4 <cmd_format_patch>, option = 1}, {cmd = 0x82d48ac "fsck", fn = 0x80cf9d5 <cmd_fsck>, option = 1}, 
  {cmd = 0x82d48b1 "fsck-objects", fn = 0x80cf9d5 <cmd_fsck>, option = 1}, {cmd = 0x82d48be "gc", 
    fn = 0x80d17fd <cmd_gc>, option = 1}, {cmd = 0x82d48c1 "get-tar-commit-id", 
    fn = 0x8163545 <cmd_get_tar_commit_id>, option = 0}, {cmd = 0x82d48d3 "grep", fn = 0x80d80ba <cmd_grep>, 
    option = 3}, {cmd = 0x82d48d8 "help", fn = 0x80dcd12 <cmd_help>, option = 0}, {cmd = 0x82d48dd "init", 
    fn = 0x80e0d5b <cmd_init_db>, option = 0}, {cmd = 0x82d48e2 "init-db", fn = 0x80e0d5b <cmd_init_db>, 
    option = 0}, {cmd = 0x82d48ea "log", fn = 0x80e4c6f <cmd_log>, option = 3}, {cmd = 0x82d48ee "ls-files", 
    fn = 0x80ef3e5 <cmd_ls_files>, option = 1}, {cmd = 0x82d48f7 "ls-tree", fn = 0x80f1e84 <cmd_ls_tree>, 
    option = 1}, {cmd = 0x82d48ff "ls-remote", fn = 0x80f0a35 <cmd_ls_remote>, option = 0}, {
    cmd = 0x82d4909 "mailinfo", fn = 0x80f99ac <cmd_mailinfo>, option = 0}, {cmd = 0x82d4912 "mailsplit", 
    fn = 0x80fbd21 <cmd_mailsplit>, option = 0}, {cmd = 0x82d491c "merge", fn = 0x81045ff <cmd_merge>, option = 5}, {
    cmd = 0x82d4922 "merge-base", fn = 0x81084c3 <cmd_merge_base>, option = 1}, {cmd = 0x82d492d "merge-file", 
    fn = 0x8108839 <cmd_merge_file>, option = 0}, {cmd = 0x82d4938 "merge-ours", fn = 0x8109594 <cmd_merge_ours>, 
    option = 1}, {cmd = 0x82d4943 "merge-recursive", fn = 0x81097ca <cmd_merge_recursive>, option = 5}, {
    cmd = 0x82d4953 "merge-subtree", fn = 0x81097ca <cmd_merge_recursive>, option = 5}, {cmd = 0x82d4961 "mktree", 
    fn = 0x810afea <cmd_mktree>, option = 1}, {cmd = 0x82d4968 "mv", fn = 0x810ba65 <cmd_mv>, option = 5}, {
    cmd = 0x82d496b "name-rev", fn = 0x810ef35 <cmd_name_rev>, option = 1}, {cmd = 0x82d4974 "pack-objects", 
    fn = 0x811daed <cmd_pack_objects>, option = 1}, {cmd = 0x82d4981 "peek-remote", fn = 0x80f0a35 <cmd_ls_remote>, 
    option = 0}, {cmd = 0x82d498d "pickaxe", fn = 0x807770d <cmd_blame>, option = 1}, {cmd = 0x82d4995 "prune", 
    fn = 0x812160f <cmd_prune>, option = 1}, {cmd = 0x82d499b "prune-packed", fn = 0x812029c <cmd_prune_packed>, 
    option = 1}, {cmd = 0x82d49a8 "push", fn = 0x8122de2 <cmd_push>, option = 1}, {cmd = 0x82d49ad "read-tree", 
    fn = 0x8123640 <cmd_read_tree>, option = 1}, {cmd = 0x82d49b7 "receive-pack", fn = 0x8128ec4 <cmd_receive_pack>, 
    option = 0}, {cmd = 0x82d49c4 "reflog", fn = 0x812ebcf <cmd_reflog>, option = 1}, {cmd = 0x82d49cb "remote", 
    fn = 0x813ad5e <cmd_remote>, option = 1}, {cmd = 0x82d49d2 "replace", fn = 0x813c0fc <cmd_replace>, option = 1}, 
  {cmd = 0x82d49da "repo-config", fn = 0x809f881 <cmd_config>, option = 0}, {cmd = 0x82d49e6 "rerere", 
    fn = 0x813d60d <cmd_rerere>, option = 1}, {cmd = 0x82d49ed "reset", fn = 0x813f0c9 <cmd_reset>, option = 1}, {
    cmd = 0x82d49f3 "rev-list", fn = 0x8142605 <cmd_rev_list>, option = 1}, {cmd = 0x82d49fc "rev-parse", 
    fn = 0x81461ab <cmd_rev_parse>, option = 0}, {cmd = 0x82d4a06 "revert", fn = 0x814c24b <cmd_revert>, 
    option = 5}, {cmd = 0x82d4a0d "rm", fn = 0x814d170 <cmd_rm>, option = 1}, {cmd = 0x82d4a10 "send-pack", 
    fn = 0x815167e <cmd_send_pack>, option = 1}, {cmd = 0x82d4a1a "shortlog", fn = 0x81547ad <cmd_shortlog>, 
    option = 2}, {cmd = 0x82d4a23 "show-branch", fn = 0x81590c0 <cmd_show_branch>, option = 1}, {
    cmd = 0x82d4a2f "show", fn = 0x80e3cc2 <cmd_show>, option = 3}, {cmd = 0x82d4a34 "status", 
    fn = 0x809a6e5 <cmd_status>, option = 5}, {cmd = 0x82d4a3b "stripspace", fn = 0x815e3e7 <cmd_stripspace>, 
    option = 0}, {cmd = 0x82d4a46 "symbolic-ref", fn = 0x815e849 <cmd_symbolic_ref>, option = 1}, {
    cmd = 0x82d4a53 "tag", fn = 0x816180b <cmd_tag>, option = 1}, {cmd = 0x82d4a57 "tar-tree", 
    fn = 0x81630ac <cmd_tar_tree>, option = 0}, {cmd = 0x82d4a60 "unpack-objects", 
    fn = 0x8166bdf <cmd_unpack_objects>, option = 1}, {cmd = 0x82d4a6f "update-index", 
    fn = 0x816b514 <cmd_update_index>, option = 1}, {cmd = 0x82d4a7c "update-ref", fn = 0x816ddd0 <cmd_update_ref>, 
    option = 1}, {cmd = 0x82d4a87 "update-server-info", fn = 0x816e734 <cmd_update_server_info>, option = 1}, {
    cmd = 0x82d4a9a "upload-archive", fn = 0x816f579 <cmd_upload_archive>, option = 0}, {
    cmd = 0x82d4aa9 "verify-tag", fn = 0x817257a <cmd_verify_tag>, option = 1}, {cmd = 0x82d4ab4 "version", 
    fn = 0x81f5c18 <cmd_version>, option = 0}, {cmd = 0x82d4abc "whatchanged", fn = 0x80e339b <cmd_whatchanged>, 
    option = 3}, {cmd = 0x82d4ac8 "write-tree", fn = 0x8172814 <cmd_write_tree>, option = 1}, {
    cmd = 0x82d4ad3 "verify-pack", fn = 0x81714a2 <cmd_verify_pack>, option = 0}, {cmd = 0x82d4adf "show-ref", 
    fn = 0x815d8b1 <cmd_show_ref>, option = 1}, {cmd = 0x82d4ae8 "pack-refs", fn = 0x811f8a4 <cmd_pack_refs>, 
    option = 1}}
 ext = ""
#5  0x0804d1ce in run_argv (argcp=0xbfabea20, argv=0xbfabea24) at git.c:436
 done_alias = 0
#6  0x0804d6d1 in main (argc=2, argv=0xbfabeaa8) at git.c:507
 cmd = 0xbfac098a "rerere"
 done_help = 0
 was_alias = 0
(gdb) quit