... in SvXMLLegacyToFastDocHandler::startElement(), so that it does not
create invalid "-1" tokens that end up stored as empty-string
attribute names in SvXMLAttrCollection and ultimately exported
as invalid XML.

The maName in struct UnknownAttribute actually stores a QName,
i.e. namespace-prefixed, since commit
bb59a80e.

The attributes are read and converted again in
SvXMLImportContext::startUnknownElement().

Change-Id: Ia69a4da293f1a84ce30766abc09ca19e2620edbd
Reviewed-on: https://gerrit.libreoffice.org/50580Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>