SvxMenuConfigPage: Disable controls when no menus found

We reuse this page for context menus, but not all modules
have context menus. This is the same behavior now as in
the toolbars page (but ideally we shouldn't show those
pages at all in such case).

Change-Id: I66e308400d50934044179f07709c371578db8c39

cui/source/customize/cfg.cxx

@@ -2635,6 +2635,9 @@ IMPL_LINK_NOARG_TYPED( SvxMenuConfigPage, SelectMenu, ListBox&, void )
     m_pContentsListBox->Clear();
 
     SvxConfigEntry* pMenuData = GetTopLevelSelection();
+    m_pModifyTopLevelButton->Enable( pMenuData != nullptr );
+    m_pModifyCommandButton->Enable( pMenuData != nullptr );
+    m_pAddCommandsButton->Enable( pMenuData != nullptr );
 
     PopupMenu* pPopup = m_pModifyTopLevelButton->GetPopupMenu();
     if ( pMenuData )