[0.13.8] Train stops instantly when it can't path

[orost]

If a train travelling in automated mode gets a "no path" error it will disregard physics and stop instantly

Reproduction:

1. create a train
2. add one stop to its schedule
3. make it start travelling to that stop
4. while it's moving, delete the stop

Train will immediately have 0 speed instead of braking normally.

[Loewchen]

That is intentional, so that the train does not roll somewhere it can not get out of.
NaB.