Nit: fix use of bufio.Scanner.Err

The Err() method should be called after the Scan() loop, not inside it.

Found by

 git grep -A3 -F '.Scan()' | grep Err

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/fs2/defaultpath.go

@@ -80,9 +80,6 @@ func parseCgroupFromReader(r io.Reader) (string, error) {
 		s = bufio.NewScanner(r)
 	)
 	for s.Scan() {
-		if err := s.Err(); err != nil {
-			return "", err
-		}
 		var (
 			text  = s.Text()
 			parts = strings.SplitN(text, ":", 3)
@@ -95,5 +92,8 @@ func parseCgroupFromReader(r io.Reader) (string, error) {
 			return parts[2], nil
 		}
 	}
+	if err := s.Err(); err != nil {
+		return "", err
+	}
 	return "", errors.New("cgroup path not found")
 }