Fix to computation of size of texture in presense of compressed textures + mipaplevels<=1
Fix to computation of size of texture in presense of compressed textures + mipaplevels<=1


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