Stargates are now finally spawned correctly

Fixes #3

cicaprojekt/Wall.java

@@ -9,7 +9,8 @@ public class Wall extends Tile {
 
     @Override
     public void spawnStargate(Stargate stargate, Direction direction) {
-        clearStargate();
+        if(stargate.isSpawned())
+            stargate.getCurrentWall().clearStargate();
         if (sg == null) {
             sg = stargate;
             sg.setCurrentWall(this);