The condition to check if to activate or deactivate the thumbnails was almost always false, because len(self._rendered_topics) < len(self.topics) will always be true if some of the topics datatypes do not support rendering.
Now, it toggles thumbnails based on the previous state of the button.
Depends on https://github.com/ros-visualization/rqt_bag/pull/116.
Fix of minor bug I found while using rqt_bag.
The condition to check if to activate or deactivate the thumbnails was almost always false, because
len(self._rendered_topics) < len(self.topics)
will always be true if some of the topics datatypes do not support rendering. Now, it toggles thumbnails based on the previous state of the button.