fix textformat without unit

dbus-goecharger.py

@@ -274,7 +274,7 @@ def main():
           '/SetCurrent': {'initial': 0, 'textformat': _a},
           '/MaxCurrent': {'initial': 0, 'textformat': _a},
           '/MCU/Temperature': {'initial': 0, 'textformat': _degC},
-          '/StartStop': {'initial': 0}
+          '/StartStop': {'initial': 0, 'textformat': lambda p, v: (str(v))}
         }
         )