btrfs: fix leaf leak in an error path in btrfs_del_items()

If the call to btrfs_del_leaf() fails we return without decrementing the
extra ref we took on the leaf, therefore leaking it. Fix this by ensuring
we drop the ref count before returning the error.

Fixes: 751a276 ("btrfs: do not BUG_ON() on tree mod log failures at btrfs_del_ptr()")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/ctree.c

@@ -4586,9 +4586,9 @@ int btrfs_del_items(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 			if (btrfs_header_nritems(leaf) == 0) {
 				path->slots[1] = slot;
 				ret = btrfs_del_leaf(trans, root, path, leaf);
+				free_extent_buffer(leaf);
 				if (ret < 0)
 					return ret;
-				free_extent_buffer(leaf);
 				ret = 0;
 			} else {
 				/* if we're still in the path, make sure