Fix the rig bounds being updated twice per frame

Unlike what I expected, the osgUtil::UpdateVisitor is set to traverse all children (not only active children). The FrameSwitch was thus traversing both RigGeometries part of the double-buffering scheme, rather than only the one active in the current frame.

components/nifosg/nifloader.cpp

@@ -100,7 +100,7 @@ namespace
 
         virtual void traverse(osg::NodeVisitor& nv)
         {
-            if (nv.getTraversalMode() != osg::NodeVisitor::TRAVERSE_ACTIVE_CHILDREN)
+            if (nv.getTraversalMode() != osg::NodeVisitor::TRAVERSE_ACTIVE_CHILDREN && nv.getVisitorType() != osg::NodeVisitor::UPDATE_VISITOR)
                 osg::Group::traverse(nv);
             else
             {