LibreOffice Corrupts DOCX files containing Footnotes after Roundtrip

	Issue :
	1] Extra data was getting written into document.xml after
           </w:document>
   	   This includes :
   		1) <sectPr> tag
   		2) Paragraph tag of <w:footnote w:id="2"> from
                   footnotes.xml
	2] This is leading to document corruption

	Implementation :
	1] Enabled a flag inside DocxAttributeOutput::FootnotesEndnotes
	2] Check value of flag to decide whehter to write section
           properties or not

Conflicts:
	sw/qa/extras/ooxmlexport/ooxmlexport.cxx
	sw/source/filter/ww8/docxattributeoutput.cxx
Reviewed on:
	https://gerrit.libreoffice.org/6644

Change-Id: Iae53fd6bf12bcbac84846bd36823bc08f21f9edf