Fix accidently empty lines in meminfo_linux (prometheus#1671)

* Fix accidently empty lines in meminfo_linux

Signed-off-by: qwertysun <qwertysun@tencent.com>

Author: alpaca2333

collector/meminfo_linux.go

@@ -45,6 +45,10 @@ func parseMemInfo(r io.Reader) (map[string]float64, error) {
 	for scanner.Scan() {
 		line := scanner.Text()
 		parts := strings.Fields(line)
+		// Workaround for empty lines occasionally occur in CentOS 6.2 kernel 3.10.90.
+		if len(parts) == 0 {
+			continue
+		}
 		fv, err := strconv.ParseFloat(parts[1], 64)
 		if err != nil {
 			return nil, fmt.Errorf("invalid value in meminfo: %s", err)