r2085: ****ertion fails after removing a station
****ertion at line 1173 in vehicle/simvehikel.cc fails.
Steps to reproduce:
1) build 3 stations
2) connect them with a convoy
3) at 1st station convoy loads freight for 2nd station
4) remove 2nd station before convoy arrives
5) when convoy arrives at 3rd station, ****ertion fails, because ware.gib_zwischenziel().is_bound().
Attached savegame (pak64) is saved between steps 3 and 4.