xfs: fix the check for COW extents in xfs_swap_extents

i_cnextents does not include delayed allocated extents, so switch
to the inode fork size check that we already use in other places
instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_bmap_util.c

@@ -2014,11 +2014,11 @@ xfs_swap_extents(
 		ip->i_cowfp = tip->i_cowfp;
 		tip->i_cowfp = cowfp;
 
-		if (ip->i_cowfp && ip->i_cnextents)
+		if (ip->i_cowfp && ip->i_cowfp->if_bytes)
 			xfs_inode_set_cowblocks_tag(ip);
 		else
 			xfs_inode_clear_cowblocks_tag(ip);
-		if (tip->i_cowfp && tip->i_cnextents)
+		if (tip->i_cowfp && tip->i_cowfp->if_bytes)
 			xfs_inode_set_cowblocks_tag(tip);
 		else
 			xfs_inode_clear_cowblocks_tag(tip);