Change: Avoid crashing to the side of a train

When a road vehicle is already running on a multi level crossing, and a train shows up ahead, don't make the road vehicle crash on the side of the train.

src/train.h

@@ -65,6 +65,8 @@ int GetTrainStopLocation(StationID station_id, TileIndex tile, const Train *v, i
 
 void GetTrainSpriteSize(EngineID engine, uint &width, uint &height, int &xoffs, int &yoffs, EngineImageType image_type);
 
+bool TrainOnCrossing(TileIndex tile);
+
 /** Variables that are cached to improve performance and such */
 struct TrainCache {
 	/* Cached wagon override spritegroup */