Return NULL unless screen number is zero. We have only one screen on

Return NULL unless screen number is zero. We have only one screen on

2005-06-05  Tor Lillqvist  <tml@novell.com>

	* gdk/win32/gdkscreen-win32.c
	(_gdk_windowing_substitute_screen_number): Return NULL unless
	screen number is zero. We have only one screen on Win32.
	(gdk_screen_make_display_name): Call gdk_display_get_name() and
	return that.