Fix an exception when a SpriteObject is added to the scene.
Fix an exception when a SpriteObject is added to the scene.

- Broken since the collisionBox was moved out of SpriteObject and into ObjectEntity.
- The fix uses the object itself as the Rect to check within the viewport; this is OK because SpriteObject inherits directly from me.Rect.

srbala/melonJS,rlugojr/melonJS,melonjs/melonJS,MarkoIvanetic/melonJS,Smoss/Enoru-eco,gopalindians/melonJS,rlugojr/melonJS,TukekeSoft/melonJS,gopalindians/melonJS,srbala/melonJS,TukekeSoft/melonJS,srbala/melonJS,MarkoIvanetic/melonJS,melonjs/melonJS,TukekeSoft/melonJS,Smoss/Enoru-eco,gopalindians/melonJS,rlugojr/melonJS