Added check against glGetString(GL_VERSION) returning NULL.
Added check against glGetString(GL_VERSION) returning NULL.


ntoand/osg,artoolkit/osg,koshman86/osg,stmh/osg,ntoand/osg,ntoand/osg,ghub/osg,XiaoCC/osg,XiaoCC/osg,stmh/osg,omega-hub/osg,XiaoCC/osg,omega-hub/osg,koshman86/osg,ghub/osg,stmh/osg,koshman86/osg,koshman86/osg,artoolkit/osg,stmh/osg,ghub/osg,XiaoCC/osg,omega-hub/osg,artoolkit/osg,omega-hub/osg,ntoand/osg,XiaoCC/osg,ghub/osg,artoolkit/osg,stmh/osg