Btrfs: check if leaf's parent exists before pushing items around

During splitting a leaf, pushing items around to hopefully get some space only
works when we have a parent, ie. we have at least one sibling leaf.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/ctree.c

@@ -3986,7 +3986,7 @@ static noinline int split_leaf(struct btrfs_trans_handle *trans,
 		return -EOVERFLOW;
 
 	/* first try to make some room by pushing left and right */
-	if (data_size) {
+	if (data_size && path->nodes[1]) {
 		wret = push_leaf_right(trans, root, path, data_size,
 				       data_size, 0, 0);
 		if (wret < 0)