Here we were accessing the notification from a destructor; so avoid that
when the pDoc is already being destructed.
Change-Id: I686bc9acf66788bfed6cf478fc7a1646ca8fd259
Reviewed-on: https://gerrit.libreoffice.org/85235
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Jan Holesovsky <kendy@collabora.com>