make it compile in the absence of GraphicsWindow::register_resize_function. Code is untested.

panda/src/glutdisplay/glutGraphicsWindow.cxx

@@ -252,10 +252,12 @@ void glutGraphicsWindow::register_idle_function(GraphicsWindow::vfn f) {
   glutIdleFunc(f);
 }
 
+/*
 void glutGraphicsWindow::register_resize_function(GraphicsWindow::vfnii f) {
   GraphicsWindow::register_resize_function(f);
   glutReshapeFunc(f);
 }
+*/
 
 void glutGraphicsWindow::main_loop(void) {
   glutMainLoop();

panda/src/glutdisplay/glutGraphicsWindow.h

@@ -90,7 +90,7 @@ public:
   virtual void flag_redisplay(void);
   virtual void register_draw_function(GraphicsWindow::vfn);
   virtual void register_idle_function(GraphicsWindow::vfn);
-  virtual void register_resize_function(GraphicsWindow::vfnii);
+  //  virtual void register_resize_function(GraphicsWindow::vfnii);
   virtual void main_loop(void);
 
   virtual TypeHandle get_gsg_type() const;