mso-test: duplicate w:sz

This is using the test document from tdf120515-1.odt.
When importing and exporting to DOCX, we generate duplicate w:sz because
we call WriteCollectedRunProperties() twice from EndRunProperties(),
but we were not clearing m_oFontSize like we clear all the other
accumulated data.

Change-Id: I1397606cd1f374e395f29a479eff860c3ebe75b0
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/193397
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Michael Stahl <michael.stahl@collabora.com>
(cherry picked from commit be8bad5cd6628d7353679045742476fa9dd66121)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/193472
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Jenkins

sw/source/filter/ww8/docxattributeoutput.cxx

@@ -3600,7 +3600,10 @@ void DocxAttributeOutput::WriteCollectedRunProperties()
     }
 
     if ( m_oFontSize )
+    {
         m_pSerializer->singleElementNS(XML_w, XML_sz, FSNS(XML_w, XML_val), OString::number(*m_oFontSize));
+        m_oFontSize.reset();
+    }
 
     if ( m_pColorAttrList.is() )
     {