CAS would never be planned for turn 0 because there were no enemy ground
units, so a breakthrough attack was planned and CAS was considered
unnecessary. Fix that by rejecting all frontline stance tasks when there
are no *friendly* ground units to command.
Another issue is that CAS missions were being planned even when there
were no enemy front line forces. Skip planning in that case except on
turn 0 since we expect there to be enemy ground units on turn 1.
Fixes https://github.com/dcs-liberation/dcs_liberation/issues/1629