rosbag - _read_message in bag.py throws exception

[rui-cai]

since melodic, the function "seek_and_read_message_data_record" has different numbers of parameters for the two classes "_BagReader102_Indexed" and "_BagReader200". Call "_read_message" directly will throw an exception when the reader is _BagReader200.

[VictorLamoine]

• See issue Does not work on Melodic ros-visualization/rqt_bag#27
• The commit 752cf1f breaks rosbag API

Exception in thread Thread-7:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rqt_bag/timeline_cache.py", line 74, in run
    msg_stamp, item = self.loader(topic, stamp, item_details)
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rqt_bag_plugins/image_timeline_renderer.py", line 160, in _load_thumbnail
    msg_topic, msg, msg_stamp = bag._read_message(pos)
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rosbag/bag.py", line 1299, in _read_message
    return self._reader.seek_and_read_message_data_record(position, raw)
TypeError: seek_and_read_message_data_record() takes exactly 4 arguments (3 given)

Exception in thread Thread-15:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rqt_bag/message_loader_thread.py", line 83, in run
    msg_data = self._get_message(bag, playhead_position)
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rqt_bag/message_loader_thread.py", line 96, in _get_message
    msg_data = self.timeline.read_message(bag, position)
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rqt_bag/bag_timeline.py", line 481, in read_message
    return bag._read_message(position)
  File "/opt/ros/melodic/lib/python2.7/dist-packages/rosbag/bag.py", line 1299, in _read_message
    return self._reader.seek_and_read_message_data_record(position, raw)
TypeError: seek_and_read_message_data_record() takes exactly 4 arguments (3 given)