The code in SvXMLExportItemMapper::exportXML was broken as far back as
its introduction in

    commit 0c28e3c4
    "Move SvXMLAttrContainerItem to SVX, moved writer only code to sw"

Change-Id: I90043ce8b7263aa56fd0883d350e29b97eeaf99b
Reviewed-on: https://gerrit.libreoffice.org/41282Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>