After calling cancel_all_goals() isNewGoalAvailable returns true

[corot]

If there was already a goal with PENDING status.
The action server cancels (correctly) both the ACTIVE and the PENDING goal, and sets new_goal_preempt_request_ to true.
But doesn't touch new_goal_, and so isNewGoalAvailable will keep returning true. This is a big problem, because on simple action server, isNewGoalAvailable is afaik the only way to tell if the current goal is being preempted (isNewGoalAvailable() == true)or canceled (isNewGoalAvailable() == false)

Of course this is not at all a new issue; the behavior seems to be that by design, but I would like to understand why. This change "fixes" the issue:

Nevertheless, even if not intended, I suppose it doesn't make much sense to PR on noetic, right?