Main: ParticleSystem - fix setMaterialName lookup
Main: ParticleSystem - fix setMaterialName lookup

previously it would arbitrarily create a default material
if given name was not found

paroj/ogre,paroj/ogre,OGRECave/ogre,OGRECave/ogre,paroj/ogre,paroj/ogre,OGRECave/ogre,OGRECave/ogre,OGRECave/ogre,paroj/ogre