The usual symptom here was the game breaking when a carrier is
destroyed. The carrier would no longer be operational but missions would
be assigned there that could not generate flight plans.
If there are not airbases withing ferry range with available parking for
the aircraft then the aircraft will be captured and sold. Otherwise the
aircraft will retreat to the closest available airbase.
Fixes https://github.com/Khopa/dcs_liberation/issues/693