DocxAttributeOutput::WriteSdtBlock: never write <w:id> twice

Change-Id: Iab68a4e809a7924e753db5a85d9914308419b845

sw/qa/extras/ooxmlexport/ooxmlfieldexport.cxx

@@ -532,6 +532,15 @@ DECLARE_OOXMLEXPORT_TEST(testSdt2Run, "sdt-2-para.docx")
     }
 }
 
+DECLARE_OOXMLEXPORT_TEST(test2Id, "2-id.docx")
+{
+    if (xmlDocPtr pXmlDoc = parseExport())
+    {
+        // This was 2, but only one w:id is allowed.
+        assertXPath(pXmlDoc, "//w:sdtPr/w:id", 1);
+    }
+}
+
 #endif
 
 CPPUNIT_PLUGIN_IMPLEMENT();

sw/source/filter/ww8/docxattributeoutput.cxx

@@ -612,7 +612,7 @@ void DocxAttributeOutput::WriteSdtBlock( sal_Int32& nSdtPrToken,
 
             m_pSerializer->endElement( nSdtPrToken );
         }
-        else if( (nSdtPrToken > 0) && !(m_bRunTextIsOn && m_rExport.SdrExporter().IsParagraphHasDrawing()))
+        else if( (nSdtPrToken > 0) && nSdtPrToken != FSNS( XML_w, XML_id ) && !(m_bRunTextIsOn && m_rExport.SdrExporter().IsParagraphHasDrawing()))
             m_pSerializer->singleElement( nSdtPrToken, FSEND );
 
         if( nSdtPrToken == FSNS( XML_w, XML_id ) || ( bPara && m_bParagraphSdtHasId ) )