Debian server: `dvb` behavior change.

Don't fail if there are no Docker volumes to backup. When running
manually it makes sense, but in the scope of a Cron job, the job fails
on hosts that don't have volumes marked for backup which is just noise.

Ansible/roles/debian_server/files/dvb

@@ -57,7 +57,6 @@ then
 elif [ -z "$(docker volume ls --filter label=snapshot=true --format '{{ .Name }}')" ]
 then
     echo "No Docker volumes marked for backup, exiting." >&2
-    exit 1
 fi
 
 dest="$1"