Aircraft Carrier stops attacking after saving the game

[bobtista]

When the Aircraft Carrier is attacking and the game is saved (without loading afterwards), the carrier stops sending out planes. The planes already in the air finish their attack run, but no new planes take off and the attack stops.

Originally reported by @xezon in #2896.

Reproduction:

1. Load USA mission 02.
2. Select the Aircraft Carrier.
3. Force fire a spot on the ground so it keeps launching planes at it.
4. Save the game (do not load).
5. The planes currently in the air fire their missiles, then no more planes launch.