fdo#81113 always run the actual detection

The old code only run detection if an UCBContent property was passed.
That means that any time the function got only InputStream, it claimed
that it was a Keynote presentation.

Change-Id: I377828229e7e95384257bde247612d7768307581
(cherry picked from commit c10390a681a4d4696d45a6d38f7d01829f368daa)
Reviewed-on: https://gerrit.libreoffice.org/10357
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>