small compile fix for ios viewer example gles1
small compile fix for ios viewer example gles1

scrawl/osg,openscenegraph/osg,scrawl/osg,openscenegraph/osg,scrawl/osg,openscenegraph/osg,jtorresfabra/osg,jtorresfabra/osg,scrawl/osg,jtorresfabra/osg,openscenegraph/osg,jtorresfabra/osg