Codechange: Use new function to get a bitmask of empty cargo types.

src/station_func.h

@@ -31,6 +31,7 @@ CargoArray GetAcceptanceAroundTiles(TileIndex tile, int w, int h, int rad, Cargo
 
 void UpdateStationAcceptance(Station *st, bool show_msg);
 CargoTypes GetAcceptanceMask(const Station *st);
+CargoTypes GetEmptyMask(const Station *st);
 
 const DrawTileSprites *GetStationTileLayout(StationType st, byte gfx);
 void StationPickerDrawSprite(int x, int y, StationType st, RailType railtype, RoadType roadtype, int image);