Code review comment for lp://staging/~3v1n0/gtk/ubuntugtk3-fix-gtkbuilder-menus

I think that this local variable is unneeded

140 ++ GtkMenuBar *menu_bar;
141 ++

But I think the approach makes sense. I'd describe it slightly differently though. Instead of using the gtk_widget_visible() function we're checking the internal shown variable as that represents the internal state instead of whether it is actually visible to the user.