xfs: fix remote xattr valuelblk check

In debugging other problems with generic/753, it turns out that it's
possible for the system go to down in the middle of a remote xattr set
operation such that the leaf block entry is marked incomplete and
valueblk is set to zero.  Make this no longer a failure.

Cc: <stable@vger.kernel.org> # v4.15
Fixes: 13791d3 ("xfs: scrub extended attribute leaf space")
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

Author: Darrick J. Wong

fs/xfs/scrub/attr.c

@@ -338,7 +338,10 @@ xchk_xattr_entry(
 		rentry = xfs_attr3_leaf_name_remote(leaf, idx);
 		namesize = xfs_attr_leaf_entsize_remote(rentry->namelen);
 		name_end = (char *)rentry + namesize;
-		if (rentry->namelen == 0 || rentry->valueblk == 0)
+		if (rentry->namelen == 0)
+			xchk_da_set_corrupt(ds, level);
+		if (rentry->valueblk == 0 &&
+		    !(ent->flags & XFS_ATTR_INCOMPLETE))
 			xchk_da_set_corrupt(ds, level);
 	}
 	if (name_end > buf_end)