fix in RenderBoxScene.cpp

Hi,

two days trying put a RenderBox into a ItemBox.

as global variable works fine:wraps::RenderBoxScene gRenderBoxScene;
but as pointer crashwraps::RenderBoxScene* a = new wraps::RenderBoxScene();

we must add the defult null value for mScene and mNode in constructor:
RenderBoxScene::RenderBoxScene() :
mCameraNode(nullptr),
mCamera(nullptr),
mEntity(nullptr),
mAnimationState(nullptr),
mRotationSpeed(RENDER_BOX_AUTO_ROTATION_SPEED),
mMouseRotation(false),
mLastPointerX(0),
mLeftPressed(false),
mAutoRotation(false),
mFrameAdvise(false),
mScene(nullptr), <---- missing line
mNode(nullptr) <---- missing line
{
}

Please, fix it in the next pack of demos.
Congratulations by the great work you are doing with this GUI

10x =)