Changed the reset of the GLExtensions::Set() in the State destructor so that it checks to see if the local _glExtensions pointer has been set up and taken ownership of the GLExtensions::Set() value

git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14661 16af8721-9629-0410-8352-f15c8da7e697

src/osg/State.cpp

@@ -132,8 +132,11 @@ State::State():
 State::~State()
 {
     // delete the GLExtensions object associated with this osg::State.
+    if (_glExtensions)
+    {
         GLExtensions::Set(_contextID, 0);
         _glExtensions = 0;
+    }
 
     //_texCoordArrayList.clear();