fdo#64283: SwMailMergeDlg: add back missing initialize

(regression from b2486241)

Change-Id: I0ed8c4ec91a095babccd089c7fe4508d123ba86d
(cherry picked from commit 61ab0ca6)

sw/source/ui/envelp/mailmrge.cxx

@@ -269,6 +269,7 @@ SwMailMergeDlg::SwMailMergeDlg(Window* pParent, SwWrtShell& rShell,
         {
             // create a frame wrapper for myself
             m_xFrame = frame::Frame::create( comphelper::getProcessComponentContext() );
+            m_xFrame->initialize( VCLUnoHelper::GetInterface ( pBeamerWin ) );
         }
         catch (const Exception&)
         {