Codechange: Use Map::Iterate() to iterate tiles

src/map.cpp

@@ -367,7 +367,7 @@ uint GetClosestWaterDistance(TileIndex tile, bool water)
 
 	if (!water) {
 		/* no land found - is this a water-only map? */
-		for (TileIndex t = 0; t < Map::Size(); t++) {
+		for (const auto t : Map::Iterate()) {
 			if (!IsTileType(t, MP_VOID) && !IsTileType(t, MP_WATER)) return 0x1FF;
 		}
 	}