fixed file not found when hwmon was not fully initialized on startup

pyfan.py

@@ -87,8 +87,13 @@ class ThermalZone:
             sysfs_f.write(str(value))
 
     def read_sysfs(self, path):
-        with open(self.build_pwm_path(path)) as sysfs_f:
-            return sysfs_f.readline()
+        try:
+            with open(self.build_pwm_path(path)) as sysfs_f:
+                return sysfs_f.readline()
+        except FileNotFoundError as err:
+            logging.getLogger("pyfan").warning(
+                "[%s] temp source not found. Not ready yet or wrong path? (%s)" % (self.name,
+                                                                                   err.strerror))
 
     def set_pwm_mode(self, path, value=1):
         self.write_sysfs(path + "_enable", value)