fdo#72947 Startcenter: handle file urls and non-file urls on a different way

Thanks Stephan Bergmann for the idea.

Change-Id: Ifdde1b7eaaefd30a176c47385bc9bfec48d5b86c
(cherry picked from commit 340e70e248824a3a4959fa1dee90c5650f257ae8)
Reviewed-on: https://gerrit.libreoffice.org/7377
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>