(svn r8294) -Fix: deleting a vehicle with shared orders, but no orders would fail to reset prev_shared and next_shared

-As a result, vehicles in the game could end up having prev/next pointers to vehicles, that was no longer in the game

src/vehicle.cpp

@@ -572,7 +572,7 @@ void DestroyVehicle(Vehicle *v)
 
 	UpdateVehiclePosHash(v, INVALID_COORD, 0);
 	v->next_hash = NULL;
-	if (v->orders != NULL) DeleteVehicleOrders(v);
+	if (IsPlayerBuildableVehicleType(v)) DeleteVehicleOrders(v);
 
 	/* Now remove any artic part. This will trigger an other
 	 *  destroy vehicle, which on his turn can remove any