[PATCH] fsck-cache segfaults on a tag referring to a missing object.

I do not understand the comment about ignoring tag reachability
in check_connectivity(), but fsck_tag() fails to notice that a
parsing of tag may have failed in the parse_object() call in
fsck_sha1() before it is called, in which case it can get a tag
object with NULL in the tagged field and segfault.  Here is a
patch to fix this.

Signed-off-by: Junio C Hamano <redacted>
---

P.S. Since this is probably more urgent than other fixes I've
been bugging you about, I am sending this via e-mail, not as a
GIT pull request, but I have a couple more update there, along
with updated HEAD.

--- a/fsck-cache.c
+++ b/fsck-cache.c

@@ -136,6 +136,12 @@ static int fsck_tag(struct tag *tag)
 	if (!show_tags)
 		return 0;
 
+	if (!tag->tagged) {
+		printf("bad referenced object in tag %s\n",
+		       sha1_to_hex(tag->object.sha1));
+		return 0;
+	}
+
 	printf("tagged %s %s",
 	       tag->tagged->type,
 	       sha1_to_hex(tag->tagged->sha1));


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