From Martin Lavery and Robert Osfield, added fallbacks for when now command line args are provided.

examples/osglight/osglight.cpp

@@ -307,7 +307,10 @@ int main( int argc, char **argv )
 
     // load the nodes from the commandline arguments.
     osg::Node* loadedModel = osgDB::readNodeFiles(arguments);
-
+    
+    // if not loaded assume no arguments passed in, try use default mode instead.
+    if (!loadedModel) loadedModel = osgDB::readNodeFile("glider.osg");
+    
     // create a room made of foor walls, a floor, a roof, and swinging light fitting.
     osg::Node* rootnode = createRoom(loadedModel);