fdo#82994: Changed filterlabel of .ac3-files

Change-Id: I7820656211e341e4d1e51821240a9319570fcffd
Reviewed-on: https://gerrit.libreoffice.org/11351
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>