btrfs: do not ignore error from btrfs_next_leaf() when inserting checksums

We are currently treating any non-zero return value from btrfs_next_leaf()
the same way, by going to the code that inserts a new checksum item in the
tree. However if btrfs_next_leaf() returns an error (a value < 0), we
should just stop and return the error, and not behave as if nothing has
happened, since in that case we do not have a way to know if there is a
next leaf or we are currently at the last leaf already.

So fix that by returning the error from btrfs_next_leaf().
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/file-item.c

@@ -889,10 +889,12 @@ int btrfs_csum_file_blocks(struct btrfs_trans_handle *trans,
 		nritems = btrfs_header_nritems(path->nodes[0]);
 		if (!nritems || (path->slots[0] >= nritems - 1)) {
 			ret = btrfs_next_leaf(root, path);
-			if (ret == 1)
+			if (ret < 0) {
+				goto out;
+			} else if (ret > 0) {
 				found_next = 1;
-			if (ret != 0)
 				goto insert;
+			}
 			slot = path->slots[0];
 		}
 		btrfs_item_key_to_cpu(path->nodes[0], &found_key, slot);