Added guard for unlabeled sensors

pywmtemp/pywmtemp.py

@@ -230,6 +230,12 @@ class SensorDockApp(wmdocklib.DockApp):
         temp = None
         temps = psutil.sensors_temperatures()
         for shw in temps.get(item.get('sensor'), []):
+            # if there is no label configured, take the first sensor
+            # temperature.
+            if not item.get('label'):
+                temp = shw
+                break
+
             if shw.label == item.get('label'):
                 temp = shw
                 break