Change wrong PROP_FILENAME to correct PROP_DIRECTORY

Change-Id: Iab2e16c486f487699e1574ed508539d95884bf9b
Reviewed-on: https://gerrit.libreoffice.org/18127Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>