fix hwmon nil ptr (prometheus#2873)

* fix hwmon nil ptr

syslink maybe lost in some cases.

---------

Signed-off-by: TaoGe <6657718+yowenter@users.noreply.github.com>
Signed-off-by: Vitaly Zhuravlev <v-zhuravlev@users.noreply.github.com>

Author: yowenter

collector/hwmon_linux.go

@@ -446,7 +446,10 @@ func (c *hwMonCollector) Update(ch chan<- prometheus.Metric) error {
 
 	for _, hwDir := range hwmonFiles {
 		hwmonXPathName := filepath.Join(hwmonPathName, hwDir.Name())
-		fileInfo, _ := os.Lstat(hwmonXPathName)
+		fileInfo, err := os.Lstat(hwmonXPathName)
+		if err != nil {
+			continue
+		}
 
 		if fileInfo.Mode()&os.ModeSymlink > 0 {
 			fileInfo, err = os.Stat(hwmonXPathName)