issue-919 Fixed "memory leak" in action clients (#920)
issue-919 Fixed "memory leak" in action clients (#920)

Whenever a call is made to `rclcpp_action::Client::wait_for_action_server`
a weak pointer to an Event object gets added to the graph_event_ vector
of the NodeGraph interface. This vector will be cleared on a node graph
change event, but if no such event occurs the weak pointer will be stuck
in the vector.  Furthermore, if client code issues repeated calls to
`wait_for_action_server` the vector will keep growing.

The fix moves the Event object creation right after the early return from
`wait_for_action_server` so that the Event object is not created in the
case that the server is known to be present and therefore there is no
need to wait for a node graph change event to occur.

Signed-off-by: Adrian Stere <33de813ec8421f0067d764c5f1a625bb53602551@clearpath.ai>
ros2/rclcpp,ros2/rclcpp