Fix #12347: Crash attempting to find catchment tiles of a station with no catchment area. (#12348)

(cherry picked from commit ea74ca0a7606d12b5ccd7cb97798a85aa87eb87d)

src/script/api/script_tilelist.cpp

@@ -158,7 +158,10 @@ ScriptTileList_StationCoverage::ScriptTileList_StationCoverage(StationID station
 {
 	if (!ScriptStation::IsValidStation(station_id)) return;
 
-	BitmapTileIterator it(::Station::Get(station_id)->catchment_tiles);
+	const BitmapTileArea &ta = ::Station::Get(station_id)->catchment_tiles;
+	if (ta.tile == INVALID_TILE) return;
+
+	BitmapTileIterator it(ta);
 	for (TileIndex tile = it; tile != INVALID_TILE; tile = ++it) {
 		this->AddTile(tile);
 	}