Fix unavailable when value is zero (#37918)

homeassistant/components/netatmo/sensor.py

@@ -555,7 +555,7 @@ class NetatmoPublicSensor(Entity):
     @property
     def available(self):
         """Return True if entity is available."""
-        return bool(self._state)
+        return self._state is not None
 
     def update(self):
         """Get the latest data from Netatmo API and updates the states."""