Fix bug for displaying all controllers (backport #1259)

[mergify]

Hi,

When using the rqt_joint_trajectory_controller, not all the controllers are shown on the controller button. This is because the list of limits was not accumulated, and only the last one was considered. This PR fixes this, showing all the valid controllers.

I hope it helps
Francisco

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This is an automatic backport of pull request #1259 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 3be3fe9 has failed:

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	both modified:   rqt_joint_trajectory_controller/rqt_joint_trajectory_controller/joint_trajectory_controller.py

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[christophfroehlich]

let's merge backport #1273 first

[mergify]

This pull request is in conflict. Could you fix it @bmagyar @destogl @christophfroehlich?