Resolves: tdf#121555 sometime crash on menu hierarchy change

seems menubar gets set to dirty due to some menu activity that needs
a refresh, but then the hierarchy changes and as its already dirty
the maUpdateMenuBarIdle doesn't get launched

the placement of the mbMenuBar test inside the loop through parents
shows some confusion as to what which mbMenuBar might be met, the
one belonging to this, or that of the parent being traversed, but
it does seem to be the one belonging to this.

Change-Id: I0b9dceadf64f7adf18eb1aa2dbda9bbfbcb66e0a
Reviewed-on: https://gerrit.libreoffice.org/65452
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

vcl/unx/gtk/gtksalmenu.cxx

@@ -226,8 +226,12 @@ void GtkSalMenu::ImplUpdate(bool bRecurse, bool bRemoveDisabledEntries)
     if (mbNeedsUpdate)
     {
         mbNeedsUpdate = false;
-        if (mbMenuBar)
+        if (mbMenuBar && maUpdateMenuBarIdle.IsActive())
+        {
             maUpdateMenuBarIdle.Stop();
+            maUpdateMenuBarIdle.Invoke();
+            return;
+        }
     }
 
     Menu* pVCLMenu = mpVCLMenu;
@@ -556,13 +560,17 @@ IMPL_LINK_NOARG(GtkSalMenu, MenuBarHierarchyChangeHandler, Timer *, void)
 void GtkSalMenu::SetNeedsUpdate()
 {
     GtkSalMenu* pMenu = this;
+    // start that the menu and its parents are in need of an update
+    // on the next activation
     while (pMenu && !pMenu->mbNeedsUpdate)
     {
         pMenu->mbNeedsUpdate = true;
-        if (mbMenuBar)
-            maUpdateMenuBarIdle.Start();
         pMenu = pMenu->mpParentSalMenu;
     }
+    // only if a menubar is directly updated do we force in a full
+    // structure update
+    if (mbMenuBar && !maUpdateMenuBarIdle.IsActive())
+        maUpdateMenuBarIdle.Start();
 }
 
 void GtkSalMenu::SetMenuModel(GMenuModel* pMenuModel)