ShapeBase::renderImage crash bug

Pretty simple one. In the change of ShapeBase::renderImage from GL to GFX, you missed the check for a null mShapeInstance. Should look like this...

void ShapeBase::renderImage(SceneState* state, SceneRenderImage* image)
{
   if ( !mShapeInstance )
     return;

   GFX->pushWorldMatrix();

   MatrixF mat = getRenderTransform();
   mat.scale( mObjScale );
   GFX->setWorldMatrix( mat );

   mShapeInstance->animate();
   mShapeInstance->render();

   GFX->popWorldMatrix();
}

This was needed when GameBase::gShowBoundingBox is enabled as it forces render images on shapes like cameras which have no shape instance.