xdemo/glxswapcontrol: Move get_framge_usage after the swap.

This fixes the problem that first frame would report bogus usage values.
Problem was caused because get_frame_usage returned data from previous buffer
swap.

Signed-off-by: Pauli Nieminen <suokkos@gmail.com>

progs/xdemos/glxswapcontrol.c

@@ -587,6 +587,9 @@ event_loop(Display *dpy, Window win)
       angle += 2.0;
 
       draw();
+
+      glXSwapBuffers(dpy, win);
+
       if ( get_frame_usage != NULL ) {
 	 GLfloat   temp;
 	 
@@ -594,8 +597,6 @@ event_loop(Display *dpy, Window win)
 	 frame_usage += temp;
       }
 
-      glXSwapBuffers(dpy, win);
-
       /* calc framerate */
       {
          static int t0 = -1;