Avoid using `save_msg_to_file(0)` for messages that don't neeed to be exported multiple times

[hect95]

Context: Due to the design of the exporter, we have to pass a 0 to save_msg_to_file(0) when exporting TFHandler and CameraInfoHandler type messages. However, this doesn't make sense as these handlers only export one message for the entire ROS bag. Fixing this will add clarity and readability to the code