Refactored spawnStargate, with default implementation in base class

cicaprojekt/Wall.java

@@ -1,18 +1,19 @@
 package cicaprojekt;
 
 public class Wall extends Tile {
-    private Stargate sg;
+    private Stargate sg = null;
 
     public Wall() {
         super();
     }
 
+    @Override
     public void spawnStargate(Stargate stargate, Direction direction) {
         clearStargate();
         if (sg == null) {
             sg = stargate;
             sg.setCurrentWall(this);
-
+            Game.instance.updateDisplay();
         }
         else
             return;