crash: unloading to multiple territories, moves allowed during history phase

[DanVanAtta]

Reported in: http://tripleadev.1671093.n2.nabble.com/crash-unloading-to-multiple-territories-tp7590987.html

1. Open any map.
2. Board two units on a single transport.
3. Unload one unit to territory A.
4. Undo.
5. Go to Show History.
6. Click on stats or any other tab besides History.
7. You can now unload one unit to territory A, despite being in history mode.
8. Show current game.
9. You can now unload the second unit to territory B, despite having already unloaded the first to territory A.
10. Undo both moves.
11. Try unloading them again and the game crashes.

[DanVanAtta]

Seems like a second bug here, not explicitly stated, is that a move action is allowed while in history mode. I've seen it before while playing. Looks like this would be a good repro case for that second problem.