sha1_file: fix delta_stack memory leak in unpack_entry

This delta_stack array can grow to any length depending on the actual
delta chain, but we forget to free it. Normally it does not matter
because we use small_delta_stack[] from stack and small_delta_stack
can hold 64-delta chains, more than standard --depth=50 in pack-objects.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -2058,6 +2058,10 @@ void *unpack_entry(struct packed_git *p, off_t obj_offset,
 	*final_size = size;
 
 	unuse_pack(&w_curs);
+
+	if (delta_stack != small_delta_stack)
+		free(delta_stack);
+
 	return data;
 }