[Vala] GTK3 HeaderBar sample fails under Windows

[simargl <archpup gmail com>]

Hi, I've downloaded gtk+-bundle_3.10.4-20131202_win32.zip from
http://win32builder.gnome.org/, installed mingw32 compiler from Arch Linux
repository and tried to compile some Vala samples for Windows. After adding
gtk3 pc file that was missing in the bundle, simple examples I tried, could
compile and worked in Wine. All, except HeaderBar. Here is that sample.

using Gtk;

class program : Gtk.Window
{
  public program()
  {
    var headerbar = new Gtk.HeaderBar();
    headerbar.show_close_button = true;

    var window = new Gtk.Window();
    window.window_position = WindowPosition.CENTER;
    window.set_default_size(200, 200);
    window.set_titlebar(headerbar);
    window.show_all();
    window.destroy.connect(Gtk.main_quit);
  }

  public static int main (string[] args)
  {
    Gtk.init(ref args);
    new program();
    Gtk.main();
    return 0;
  }
}

Error message when running this with Wine or in Windows is this:

Gtk:ERROR:gtkwindow.c:3532:gdk_window_enable_csd: assertion failed: (visual
!= NULL)