Loads message if the given type from the reader.
        Supports reading directly to existing message.

        :param msg_type:
        :param msg:
        :return:

async def load_message(self, msg_type, msg=None):
        """
        Loads message if the given type from the reader.
        Supports reading directly to existing message.

        :param msg_type:
        :param msg:
        :return:
        """
        msg = msg_type() if msg is None else msg
        fields = msg_type.f_specs() if msg_type else msg.__class__.f_specs()
        for field in fields:
            await self.message_field(msg, field)

        return msg