SwPostItField::dumpAsXml: survive 0 mpText

And no need to copy it to be able to dump it.

Change-Id: I5c0782c489a5d7c24173a81cc82efd195c4aa56e

sw/source/core/fields/docufld.cxx

@@ -1841,8 +1841,9 @@ void SwPostItField::dumpAsXml(xmlTextWriterPtr pWriter) const
     SwField::dumpAsXml(pWriter);
 
     xmlTextWriterStartElement(pWriter, BAD_CAST("mpText"));
-    OutlinerParaObject aParaObject(*mpText);
-    aParaObject.dumpAsXml(pWriter);
+    xmlTextWriterWriteFormatAttribute(pWriter, BAD_CAST("ptr"), "%p", mpText);
+    if (mpText)
+        mpText->dumpAsXml(pWriter);
     xmlTextWriterEndElement(pWriter);
 
     xmlTextWriterEndElement(pWriter);