Process callbacks from the queue populated by &listen.

def _thread_worker(self):
        """Process callbacks from the queue populated by &listen."""
        while self._running:
            # Retrieve next cmd, or block
            packet = self._queue.get(True)
            if isinstance(packet, dict) and QS_CMD in packet:
                try:
                    self._callback_listen(packet)
                except Exception as err:  # pylint: disable=broad-except
                    _LOGGER.error("Exception in callback\nType: %s: %s",
                                  type(err), err)
            self._queue.task_done()