Fixed an error causing a null pointer to be thrown

src/main/java/bitsplease/mummymayhem/model/buildings/Tower.java

@@ -51,7 +51,7 @@ public class Tower extends Sprite {
     }
 
     public Tower(TowerType type) {
-        super(type.getImagePath());
+        super(new Point2D(0,0), type.getImagePath());
         this.attack = type.getAttack();
         this.hp = type.getHp();
         this.range = type.getRange();