RA Fixed-Wing State Machine Bug

[ChthonVII]

In the REGROUP block of AircraftClass::Mission_Hunt() it's possible to call Enter_Idle_Mode() and then the code continues on potentially doing stuff inconsistent with having just done that. One branch will call Enter_Idle_Mode() as second time. Another branch will set the Status variable even though the plane now has a new mission with a different enum for what Status means. A third branch changes the mission again. See this commit.