Green line left on map when Copter's guided mode using velocity control


This happens when the vehicle is no longer providing a Location target (see Copter's get_wp() method).

To recreate the issue in SITL:

1. start SITL as a copter
2. GUIDED
3. arm throttle
4. takeoff 10
5. Right-mouse-button-click on the map and select "FlyTo", set Alt to "10" and press OK
6. Loiter (as the vehicle is moving to the target)
7. rc 1 1800 (to fly right a bit to get off the green line)

Reproduce the issue in SITL using the listed Copter GUIDED, FlyTo, Loiter, and RC steps, then inspect the map behavior when Copter no longer provides a Location target through get_wp(). Done means the green line is removed or cleared when that target is no longer available.

Written by the indexing model from the issue text.