Calling cancel blocks the controller

[rokusottervanger]

A call to cancel should return whether or not the controller implements stopping behavior. If false, the base class handles it (and outputs a zero velocity setpoint right away). Meaning we should not block, but return true immediately, in this case.

Source: https://github.com/magazino/move_base_flex/blob/a5c19cb8f3135679e4f8f36a9ec6123b121d69ab/mbf_abstract_nav/src/abstract_controller_execution.cpp#L257-L259