and if there is no videosink then give up

Change-Id: I6b60e7be1e77dbf5c4c277ccf47a4d121f3cd6a5
Reviewed-on: https://gerrit.libreoffice.org/72871Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
Reviewed-on: https://gerrit.libreoffice.org/73087Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
Tested-by: Jenkins