Ros2 port: If an invalid message type is specified, rqt_publisher will cause rqt_gui will crash

[brawner]

Traceback (most recent call last):
  File "/Users/brawner/workspace/ros2_ws/install/rqt_publisher/lib/python3.7/site-packages/rqt_publisher/publisher.py", line 90, in add_publisher
    self._add_publisher(publisher_info)
  File "/Users/brawner/workspace/ros2_ws/install/rqt_publisher/lib/python3.7/site-packages/rqt_publisher/publisher.py", line 118, in _add_publisher
    msg_module = getattr(module, message_name)
AttributeError: module 'std_msgs.msg' has no attribute 'Int32[]'