Fix vehicle despawning bug

[freeborough]

The addition of walls to the edge of the world has caused the vehicle de-spawning to fail, as the vehicles can't get to the end of the road tile they're on and therefore don't despawn.

It's potentially a tricky problem to solve, whilst keeping the wall, so will need some messing about to work out the best solution.

[freeborough]

It's not the walls, they're despawning when they hit them.