Openapoc: Vehicles don't return home after UFO invasion + base defense

[BeornTB]

336 Vehicles dont return to base.zip

First UFO invasion dropped aliens right into the base, had a base defense which went smoothly and ended without CTD.

However, I came back to frozen ships on "blue arrow" orders as if the UFOs were up. The return base button works though, so it's minor.

[FilmBoy84]

In tandem with this issue #306 needs to be implemented for full vanilla behavior