Fix a problem with statics disappearing sometimes on the map

Ogre::StaticGeometry doesn't seem to like materials being changed at runtime. It stores raw pointers to Ogre::Technique objects also, which conflicts with shiny's way of managing "unloaded" materials as having zero techniques. If a static geometry object is baked from an unloaded material, it won't find any techniques to use and can't render. By moving the unload call afterwards, it will be detected as in use by a renderable and won't be unloaded. Ideally this needs fixing of Ogre::StaticGeometry to not hold on to Technique objects (they also currently need to be rebuilt whenever user settings are changed, which also causes "unloading" of materials)