Merge pull request #17 from VGVentures/fix/ball-spawn

fix: changing ball spawning point to avoid context errors

lib/game/pinball_game.dart

@@ -18,10 +18,15 @@ class PinballGame extends Forge2DGame with FlameBloc {
 
   @override
   Future<void> onLoad() async {
-    spawnBall();
     addContactCallback(BallScorePointsCallback());
 
     await add(BottomWall(this));
     addContactCallback(BottomWallBallContactCallback());
   }
+
+  @override
+  void onAttach() {
+    super.onAttach();
+    spawnBall();
+  }
 }