[GtkGLExt] Gdk::GL::Config::create crash

[Philipp Klaus Krause <pkk spth de>]

My program crashes on

Glib::RefPtr<Gdk::GL::Config> glconfig;
glconfig = Gdk::GL::Config::create(Gdk::GL::MODE_RGB |
Gdk::GL::MODE_DEPTH | Gdk::GL::MODE_DOUBLE);

with a X error

The error was 'BadColor (invalid Colormap parameter)'.
  (Details: serial 296 error_code 12 request_code 1 minor_code 0)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

It worked before, but I'm not sure what I changed to trigger the problem
(I modiefied the program a bit and updated my X server).

Philipp