Get In vehicle action can be reserved by absent rock raiders

[trigger-segfault]

Describe the issue
It's possible to lock a vehicle in a state where no rock raider will want to get in it. But when teleporting down new rock raiders, one of them might suddenly find that idea appealing. A vehicle with this state will have the Get In icon grayed out.

Expected behaviour
Commanding a rock raider to get in the vehicle should have at least one viable unit go to get in the vehicle (Shinji get in the robot).

Steps to reproduce

1. Select a rock raider, and tell them specifically to get in a vehicle (the vehicle can optionally already be occupied).
2. Teleport up the same rock raider before they have a chance of getting in.
3. If the vehicle is occupied. Kick out the current driver.
4. Select the vehicle and the Get In icon should be grayed out. Telling other units to get in the vehicle will have them ignore the order like nothing ever happened.
5. Teleport down rock raiders until the one you originally teleported down is recalled, they will immediately go to get in the vehicle.

Additional information

• Time played this session: ~20-40 minutes.
• Level: Driller Night! (NoNerps enabled)
• Game speed: 100%
• Graphics fix: dgVoodoo 2.55.4
• Using mods: None

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Additional context (optional)
It seems that the one commanded to get in the vehicle will be teleported down in stack-order. So if you teleported up X rock raiders after teleporting up the new driver, then you'll need to teleport down X+1 rock raiders to find our driver.

This test was performed with almost all existing rock raiders being upgraded/trained in driving.