Fixes map editor crash on changing terrain of invalid tiles

mapeditor/scenelayer.cpp

@@ -461,10 +461,8 @@ void SelectionTerrainLayer::select(const std::vector<int3> & tiles)
 {
 	for (int3 tile : tiles)
 	{
-		if(!area.count(tile))
-		{
+		if(!area.count(tile) && map->isInTheMap(tile))
 			area.insert(tile);
-		}
 	}
 	redraw(tiles);
 	onSelection();