sparse-index: fix crash in status

Copy the `index_state->dir_hash` back to the real istate
after expanding a sparse index.

A crash was observed in `git status` during some hashmap lookups with
corrupted hashmap entries.  During an index expansion, new cache-entries
are added to the `index_state->name_hash` and the `dir_hash` in a
temporary `index_state` variable `full`.  However, only the `name_hash`
hashmap from this temp variable was copied back into the real `istate`
variable.  The original copy of the `dir_hash` was incorrectly preserved.
If the table in the `full->dir_hash` hashmap were realloced, the
stale version (in `istate`) would be corrupted.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

Author: jeffhostetler

sparse-index.c

@@ -295,6 +295,7 @@ void ensure_full_index(struct index_state *istate)
 
 	/* Copy back into original index. */
 	memcpy(&istate->name_hash, &full->name_hash, sizeof(full->name_hash));
+	memcpy(&istate->dir_hash, &full->dir_hash, sizeof(full->dir_hash));
 	istate->sparse_index = 0;
 	free(istate->cache);
 	istate->cache = full->cache;