name-hash.c: always initialize dir_next pointer

Test t2021-checkout-overwrite.sh reveals a segfault in 'git add' on a case-insensitive file system when git is compiled with XMALLOC_POISON defined. The reason is that 2548183b (fix phantom untracked files when core.ignorecase is set) added a new member dir_next to struct cache_entry, but forgot to initialize it in all cases.

---
You can also insert git config core.ignorecase true before the first test script in t2021 to see the segfault.

I actually found the crash with an MSVC debug build, which has something like XMALLOC_POISON built-in.

 name-hash.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index 225dd76..d8d25c2 100644
@@ -74,7 +74,7 @@ static void hash_index_entry(struct index_state *istate, struct cache_entry *ce)
 	if (ce->ce_flags & CE_HASHED)
 		return;
 	ce->ce_flags |= CE_HASHED;
-	ce->next = NULL;
+	ce->next = ce->dir_next = NULL;
 	hash = hash_name(ce->name, ce_namelen(ce));
 	pos = insert_hash(hash, ce, &istate->name_hash);
 	if (pos) {

1.7.7.1.586.ga0958b

Thanks.

Yikes, thanks.

-Peff