xfs: check _btree_check_block value

Check the _btree_check_block return value for the firstrec and lastrec
functions, since we have the ability to signal that the repositioning
did not succeed.

Fixes-coverity-id: 114067
Fixes-coverity-id: 114068
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>

fs/xfs/libxfs/xfs_btree.c

@@ -728,7 +728,8 @@ xfs_btree_firstrec(
 	 * Get the block pointer for this level.
 	 */
 	block = xfs_btree_get_block(cur, level, &bp);
-	xfs_btree_check_block(cur, block, level, bp);
+	if (xfs_btree_check_block(cur, block, level, bp))
+		return 0;
 	/*
 	 * It's empty, there is no such record.
 	 */
@@ -757,7 +758,8 @@ xfs_btree_lastrec(
 	 * Get the block pointer for this level.
 	 */
 	block = xfs_btree_get_block(cur, level, &bp);
-	xfs_btree_check_block(cur, block, level, bp);
+	if (xfs_btree_check_block(cur, block, level, bp))
+		return 0;
 	/*
 	 * It's empty, there is no such record.
 	 */