SceneNode::removeAndDestroyAllChildren: fix usage of invalid end() iter
SceneNode::removeAndDestroyAllChildren: fix usage of invalid end() iter

resolves https://ogre3d.atlassian.net/projects/OGRE/issues/OGRE-577

RealityFactory/ogre,RealityFactory/ogre,RealityFactory/ogre,RealityFactory/ogre,RealityFactory/ogre