tdf#76197 Make OfficeMenuBar work again in the start center

Regression of 46666a77.
The code in MenuBarManager::FillMenuManager merges the
addon menu before .uno:WindowList, which doesn't exist
in the start center since that commit.

As a last resort, let's also check for .uno:HelpMenu
(assuming that it's never placed before the Window menu).

Change-Id: If45eebe4351c40d8ed69daba527844ffc02e8458
Reviewed-on: https://gerrit.libreoffice.org/18729Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>
(cherry picked from commit f30206f6)

framework/source/uielement/menubarmanager.cxx

@@ -1138,7 +1138,8 @@ void MenuBarManager::FillMenuManager( Menu* pMenu, const Reference< XFrame >& rF
         {
             sal_uInt16          nItemId  = pMenu->GetItemId( nPos );
             OUString aCommand = pMenu->GetItemCommand( nItemId );
-            if ( nItemId == SID_MDIWINDOWLIST || aCommand == aSpecialWindowCommand)
+            if ( nItemId == SID_MDIWINDOWLIST || aCommand == aSpecialWindowCommand ||
+                 nItemId == SID_HELPMENU || aCommand == aCmdHelpMenu )
             {
                 // Retrieve addon popup menus and add them to our menu bar
                 framework::AddonMenuManager::MergeAddonPopupMenus( rFrame, nPos, static_cast<MenuBar *>(pMenu), m_xContext );