Fixes for zigbee devices polling

- Don't publish a `get` request if the device has no exposed queriable
  attributes.

- Perform the recursive build of the `get` request payload before
  checking for the `access` attribute.

platypush/backend/zigbee/mqtt/__init__.py

@@ -246,10 +246,12 @@ class ZigbeeMqttBackend(MqttBackend):
                 self.bus.post(ZigbeeMqttDeviceConnectedEvent(device=name, **event_args))
 
             exposes = (device.get('definition', {}) or {}).get('exposes', [])
-            client.publish(
-                self.base_topic + '/' + name + '/get',
-                json.dumps(self._plugin.build_device_get_request(exposes)),
-            )
+            payload = self._plugin.build_device_get_request(exposes)
+            if payload:
+                client.publish(
+                    self.base_topic + '/' + name + '/get',
+                    json.dumps(payload),
+                )
 
         devices_copy = [*self._devices.keys()]
         for name in devices_copy:

platypush/plugins/zigbee/mqtt/__init__.py

@@ -716,6 +716,9 @@ class ZigbeeMqttPlugin(MqttPlugin):  # lgtm [py/missing-call-to-init]
     @staticmethod
     def build_device_get_request(values: List[Dict[str, Any]]) -> dict:
         def extract_value(value: dict, root: dict):
+            for feature in value.get('features', []):
+                extract_value(feature, root)
+
             if not value.get('access', 1) & 0x4:
                 # Property not readable/query-able
                 return
@@ -729,9 +732,6 @@ class ZigbeeMqttPlugin(MqttPlugin):  # lgtm [py/missing-call-to-init]
                 root[value['property']] = root.get(value['property'], {})
                 root = root[value['property']]
 
-            for feature in value['features']:
-                extract_value(feature, root)
-
         ret = {}
         for value in values:
             extract_value(value, root=ret)