midx: fix broken free() in close_midx()

When closing a multi-pack-index, we intend to close each pack-file
and free the struct packed_git that represents it. However, this
line was previously freeing the array of pointers, not the
pointer itself. This leads to a double-free issue.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

midx.c

@@ -190,7 +190,7 @@ static void close_midx(struct multi_pack_index *m)
 	for (i = 0; i < m->num_packs; i++) {
 		if (m->packs[i]) {
 			close_pack(m->packs[i]);
-			free(m->packs);
+			free(m->packs[i]);
 		}
 	}
 	FREE_AND_NULL(m->packs);