Trucks prioritize unattended excavators

Sometimes multiple trucks will line up behind an excavator, while a different excavator is awaiting a truck to load. Trucks should only queue up for excavators if there are no unattended excavators.
They just look so lonely.

I think they do already, but once assigned, they do not react if situation changes. The better fix would be to reevaluate assignments of tower's trucks every time one of the tower excavator calls for pickup.