Also allow rect to go out of screen at the bottom

Otherwise some gaps at the very bottom are extremely hard to get.

GameScreen.java

@@ -79,7 +79,7 @@ class GameScreen implements LinearColorAnimator.AnimationListener
 
         Rectangle birdRect = _bird.getRect();
         if (_world.checkCollision(_bird.getRect())
-                || birdRect.getY() + birdRect.getHeight() > TurtleWelt.HEIGHT
+                || birdRect.getY() > TurtleWelt.HEIGHT
                 || birdRect.getY() + birdRect.getHeight() < 0)
         {
             System.out.print("\n");