add_delta_base_cache: use list_for_each_safe

We may remove elements from the list while we are iterating,
which requires using a second temporary pointer. Otherwise
stepping to the next element of the list might involve
looking at freed memory (which generally works in practice,
as we _just_ freed it, but of course is wrong to rely on;
valgrind notices it).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -2187,11 +2187,11 @@ static void add_delta_base_cache(struct packed_git *p, off_t base_offset,
 	void *base, unsigned long base_size, enum object_type type)
 {
 	struct delta_base_cache_entry *ent = xmalloc(sizeof(*ent));
-	struct list_head *lru;
+	struct list_head *lru, *tmp;
 
 	delta_base_cached += base_size;
 
-	list_for_each(lru, &delta_base_cache_lru) {
+	list_for_each_safe(lru, tmp, &delta_base_cache_lru) {
 		struct delta_base_cache_entry *f =
 			list_entry(lru, struct delta_base_cache_entry, lru);
 		if (delta_base_cached <= delta_base_cache_limit)