song_save: don't call tag_free(NULL)

When a song was in the database twice (which shouldn't happen), and
the first song had no tag items, MPD calledd tag_free(NULL).  Add a
check to that source location, and an assertion to tag_free().

1 files changed, 2 insertions, 0 deletions

diff --git a/src/tag.c b/src/tag.c
index a75ef6ba5..34205d20d 100644
--- a/src/tag.c
+++ b/src/tag.c
@@ -163,6 +163,8 @@ void tag_free(struct tag *tag)
 {
 	int i;
 
+	assert(tag != NULL);
+
 	g_mutex_lock(tag_pool_lock);
 	for (i = tag->num_items; --i >= 0; )
 		tag_pool_put_item(tag->items[i]);