receiver: only close existing devices for receiver

lib/logitech_receiver/receiver.py

@@ -99,6 +99,7 @@ class Receiver:
     def close(self):
         handle, self.handle = self.handle, None
         for _n, d in self._devices.items():
+            if d:
                 d.close()
         self._devices.clear()
         return (handle and _base.close(handle))