Encode message to AMQP wire-encoded bytearray.

        :rtype: bytearray

def encode_message(self):
        """Encode message to AMQP wire-encoded bytearray.

        :rtype: bytearray
        """
        if not self._message:
            raise ValueError("No message data to encode.")
        cloned_data = self._message.clone()
        self._populate_message_attributes(cloned_data)
        encoded_data = []
        c_uamqp.get_encoded_message_size(cloned_data, encoded_data)
        return b"".join(encoded_data)