bug#72986: Disabling menu-bar-mode changes size of new frames

[martin rudalics via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

 > Now the change_frame_size(5) initial and final sizes look correct.

OK.  In the next step I'd like to isolate the menubar code as the sole
culprit for what's going in.  Please with master do

(setq default-frame-alist '((width . 200)))

or some other insanely large value so we can see whether we can make the
GTK error disappear this way.  And please apply the trivial patch

diff --git a/src/xfns.c b/src/xfns.c
index 3f0d8f3fcd0..c90ac9c0d37 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -5230,7 +5230,7 @@ DEFUN ("x-create-frame", Fx_create_frame, Sx_create_frame,

    gui_default_parameter (f, parms, Qmenu_bar_lines,
                           NILP (Vmenu_bar_mode)
-                         ? make_fixnum (0) : make_fixnum (1),
+                         ? make_fixnum (0) : make_fixnum (0),
                           NULL, NULL, RES_TYPE_NUMBER);
    gui_default_parameter (f, parms, Qtab_bar_lines,
                           NILP (Vtab_bar_mode)
@@ -5342,7 +5342,7 @@ DEFUN ("x-create-frame", Fx_create_frame, Sx_create_frame,

  #if defined (USE_X_TOOLKIT) || defined (USE_GTK)
    /* Create the menu bar.  */
-  if (!minibuffer_only && FRAME_EXTERNAL_MENU_BAR (f))
+  if (0) // !minibuffer_only && FRAME_EXTERNAL_MENU_BAR (f))
      {
        /* If this signals an error, we haven't set size hints for the
  	 frame and we didn't make it visible.  */

and do C-x 5 2.

martin