mountinfo: move s.Err() out of scanner loop

The previous code would actually ignore IO errors during scanning,
becuase s.Scan() returns false if there was an error (leaving the loop
and never being detected). Indeed the correct way[1] of using the
builtin bufio.Scanner is actually more like:

  s := bufio.NewScanner(...)
  for s.Scan() {
      // use s.Text()
  }
  if err := s.Err(); err != nil {
      return err
  }

[1]: https://blog.golang.org/errors-are-values

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

Author: cyphar

mountinfo/mountinfo_linux.go

@@ -18,11 +18,9 @@ import (
 func GetMountsFromReader(r io.Reader, filter FilterFunc) ([]*Info, error) {
 	s := bufio.NewScanner(r)
 	out := []*Info{}
-	var err error
 	for s.Scan() {
-		if err = s.Err(); err != nil {
-			return nil, err
-		}
+		var err error
+
 		/*
 		   See http://man7.org/linux/man-pages/man5/proc.5.html
 
@@ -133,6 +131,9 @@ func GetMountsFromReader(r io.Reader, filter FilterFunc) ([]*Info, error) {
 			break
 		}
 	}
+	if err := s.Err(); err != nil {
+		return nil, err
+	}
 	return out, nil
 }