mvUserData is still needed to keep it's content from being deleted.
Revert "Drop unused instance variable."
This reverts commit 687ae6ca01.
Change-Id: I689cfdaf8d4d62a3b53ff7fb318dc8c70b9e1c2d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/167020
Reviewed-by: Thorsten Behrens <thorsten.behrens@allotropia.de>
Tested-by: Jenkins