Re: [PATCH v2 08/24] midx: respect 'core.multiPackIndex' when writing

When writing a new multi-pack index, write_midx_internal() attempts to
load any existing one to fill in some pieces of information. But it uses
load_multi_pack_index(), which ignores the configuration
"core.multiPackIndex", which indicates whether or not Git is allowed to
read an existing multi-pack-index.

Replace this with a routine that does respect that setting, to avoid
reading multi-pack-index files when told not to.

This avoids a problem that would arise in subsequent patches due to the
combination of 'git repack' reopening the object store in-process and
the multi-pack index code not checking whether a pack already exists in
the object store when calling add_pack_to_midx().

This would ultimately lead to a cycle being created along the
'packed_git' struct's '->next' pointer. That is obviously bad, but it
has hard-to-debug downstream effects like saying a bitmap can't be
loaded for a pack because one already exists (for the same pack).

Signed-off-by: Taylor Blau <redacted>
---
 midx.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/midx.c b/midx.c
index 40eb7974ba..759007d5a8 100644
--- a/midx.c
+++ b/midx.c

@@ -908,8 +908,18 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 
 	if (m)
 		ctx.m = m;
-	else
-		ctx.m = load_multi_pack_index(object_dir, 1);
+	else {