Fix crash loading tracks when shaders are disabled

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@14930 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/graphics/irr_driver.cpp

@@ -2161,7 +2161,7 @@ scene::ISceneNode *IrrDriver::addLight(const core::vector3df &pos, float energy,
     }
     else
     {
-        return NULL;
+		return m_scene_manager->addLightSceneNode(m_scene_manager->getRootSceneNode(), pos, video::SColor(1., r, g, b));
     }
 }