Fixed then normal smoothing function in the .3ds loader and the

osgUtil::SmoothingVisitor so that unused normals at left at 0,0,0 insead
of being normalized, which results in (nan,nan,nan).

src/osgUtil/SmoothingVisitor.cpp

@@ -119,7 +119,8 @@ void SmoothingVisitor::smooth(osg::GeoSet& gset)
 
         for(j = 0; j < ncoords; j++ )
         {
-            norms[j].normalize();
+            float len = norms[j].length();
+            if (len) norms[j]/=len;
         }
 
         gset.setNormalBinding(osg::GeoSet::BIND_PERVERTEX);