Don't call glutDestroyWindow() function from exit callback.

Fixed error during exit from 'crack-attack --solo':

[c0der@rock ~]$ crack-attack --solo

Crack Attack! v1.1.14

freeglut (crack-attack): Unable to create direct context rendering for window 'Crack Attack!'

This may hurt performance.

freeglut  ERROR:  Function <glutDestroyWindow> called without first calling 'glutInit'.

See for details:

https://savannah.nongnu.org/bugs/?15821

http://cvs.savannah.nongnu.org/viewvc/crack-attack/crack-attack/src/Displayer.cxx?r1=1.11&r2=1.12

--- crack-attack/src/Displayer.cxx	2006/07/19 10:24:18	1.11

+++ crack-attack/src/Displayer.cxx	2006/08/11 23:21:42	1.12

@@ -191,7 +191,6 @@

 void Displayer::cleanUp (   )

 {

-  glutDestroyWindow(main_window);

   for (int n = DC_NUMBER_USE_GARBAGE_TEX; n--; )

     if (garbage_texture_data[n] != null) {

       delete [] garbage_texture_data[n];