From Geoff Michel, fixed the handling of zfar values of 0.0.

src/osgUtil/CullVisitor.cpp

@@ -595,9 +595,9 @@ bool CullVisitor::updateCalculatedNearFar(const osg::Matrix& matrix,const osg::D
         }
     }
 
-    if (d_far<0.0)
+    if (d_far<=0.0) // gwm if ==0 extends purely behind eye, forces far to 0 get invalid projection matrix (ratio near:far=inf)
     {
-        // whole object behind the eye point so disguard
+        // whole object behind the eye point so discard
         return false;
     }