the xlink:type attribute is mandatory, related fdo#79449

Change-Id: I03c4217f786bc10aa915780dc10ea52d94019b6e
Reviewed-on: https://gerrit.libreoffice.org/13356
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>