Train cars disappear without a trace when rebuild the depot

Issue description

Don't rebuild train depot!
If you got the depot full with train cars accumulated, they will not be moved to new train depot automaticly. So you have to build useless trains and send em to new deopt.

Reproduction steps

1. Dismantle some trains - you got cars
2. Build new depot
3. Destruct old depot
4. You lost all cars

Game version and build number

v0.8.2a b552

Operating system

Windows