rqt_joint_trajectory_controller does not subscibe to /robot_description

[christophfroehlich]

Describe the bug
rqt_joint_trajectory_controller is broken in my setup. Can anyone reproduce this?

Having a look into the code, the issue is that no /robot_description is received.

Nevertheless: If there is no /robot_description publisher, an infinite number of subsribers will be created. This would be an easy fix, but I can't test it without a successful subscription.

To Reproduce
Steps to reproduce the behavior:

1. Launch example_1: ros2 launch ros2_control_demo_example_1 rrbot.launch.py
2. Activate joint_trajectory_position_controller
3. Run ros2 run rqt_joint_trajectory_controller rqt_joint_trajectory_controller
4. Select controller_manager
5. Now it's not possible to select the JTC
6. Run ros2 topic info /robot_description: Subscription count increases

Expected behavior
JTC can be selected, only one subscriber if no '/robot_description'

Environment (please complete the following information):

• OS: ubuntu 22.04
• Version rolling, built from source