docx export: add missing arg to impl_pageBorders call

The missing argument could cause data loss due to ill-formatted
document produced.

Change-Id: I65dee7f42c633ae9602d454e2f03ebc821c9c0ab

sw/source/filter/ww8/docxattributeoutput.cxx

@@ -4474,7 +4474,7 @@ void DocxAttributeOutput::FormatBox( const SvxBoxItem& rBox )
         m_pSerializer->startElementNS( XML_w, XML_pBdr, FSEND );
     }
 
-    impl_pageBorders( m_pSerializer, rBox, false, false );
+    impl_pageBorders( m_pSerializer, rBox, XML_pBdr, false, false );
 
     if ( m_bOpenedSectPr )
     {