tdf#123476 filter: Also handle empty ODF

tdf#123476 filter: Also handle empty ODF

This builds on top of commit ada07f303e7cd1e39c73abe0741aefe7d9d73a57,
to allow 0-byte ODT, ODS etc.

Possible TODO would be somehow use default template for such empty files,
getting the template name using SfxObjectFactory::GetStandardTemplate.
That would enable using 0-byte ODF files as means to "create new document
at this location from default template" workflow.

Change-Id: I36e07b80f60c42aecdcc6a7357e5bdd18f62e4f7
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/109989
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
(cherry picked from commit 2854362f429e476d4a1ab4759c6a1f1c04150280)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/110061
Tested-by: Jenkins CollaboraOffice <jenkinscollaboraoffice@gmail.com>
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>