VRP example: dueTime curtailing doesn't work with multiple depots with different dueTime's

In the swing examples, this trick curtails the dueTime of every Customer in the VRP importer, so that
customer.dueTime = Math.min(customer.dueTime, depot.dueTime - drivingTime(customer, depot))
This way, the dueTime of the Depot is respected implicitly.

https://github.com/kiegroup/optaplanner/blob/master/optaplanner-examples/src/main/java/org/optaplanner/examples/vehiclerouting/persistence/VehicleRoutingImporter.java#L515

However, when there are multiple depots with different dueTimes, this is incorrect.
We should have a proper constraint check that.