Take-off and RTL commands have icon on map

Take-off and RTL commands, although NAV commands, do not take a lat, lon position (and RTL doesn't even take an altitude). The display on the map of the line to lat,lon (0,0) position is distracting.

Trace the map rendering path for Take-off and RTL NAV commands and inspect how their command coordinates are interpreted. Confirm the behavior with these commands on the map; done means they no longer display a line or icon at the invalid (0,0) position.

Written by the indexing model from the issue text.