This is a corner case that happens when the user wants to command an
altitude change just after a takeoff. Takeoff doesn't set the current
lat and lon therefore the user had to change altitude twice to get it working.
The first time to set the current lat and lon and the second time to
actually change altitude.
Before this check we were free to fly outside of a geofence with a goto
command. With this check we ignore the command if the location of the goto
is outside the fence. If this is the case we send back a mavlink warning to
the ground station.
daniele