Even if the slot is already read out, we may still need to re-balance
the tree, thus it can cause error in that btrfs_del_item() call and we
need to handle it properly.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: void0red <void0red@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>