added method Tile.isSteppable() for obvious reasons...

cicaprojekt/Wall.java

@@ -18,6 +18,14 @@ public class Wall extends Tile {
             return;
     }
 
+    @Override
+    public boolean isSteppable() {
+        if (sg != null)
+            return true;
+
+        return false;
+    }
+
     public void clearStargate() {
         if(sg != null) {
             sg.setCurrentWall(null);