Error calling cancel_goal() in simple state DONE

[martiniil]

Using a SimpleActionClient, I would like to be able to cancel a goal with minimal delay. But using cancel_goal() sometimes yields the following error:

Received comm state PREEMPTING when in simple state DONE with SimpleActionClient in NS /sequence_move_group

This is due to the action client transitioning from DONE -> WAITING_FOR_CANCEL_ACK. In my opinion this should not happen. (which would be in accordance with the figure of the state transitions: http://wiki.ros.org/actionlib/DetailedDescription).

[jschleicher]

Probably one would want a similar check as in cpp 3db5a80d2363ddef4ffb0abc4d5bcb44c8670708 for the python client. The python client lacks such a "ignore cancel request" section https://github.com/ros/actionlib/blob/7c1833418c52ef857fbd2aae9954ccc3796b42a6/src/actionlib/action_client.py#L139