Added handling of empty slides and layers
Added handling of empty slides and layers

tomasthoresen/osg,openscenegraph/osg,jtorresfabra/osg,tomasthoresen/osg,tomasthoresen/osg,marchelbling/osg,jtorresfabra/osg,openscenegraph/osg,jtorresfabra/osg,marchelbling/osg,marchelbling/osg,scrawl/osg,scrawl/osg,marchelbling/osg,openscenegraph/osg,scrawl/osg,tomasthoresen/osg,openscenegraph/osg,jtorresfabra/osg,scrawl/osg