Ignore frames without names, becuase the code does not handle
them well. It does not affect those use case for which the
deduplication code was added.

Change-Id: I08ad062b8b11cc06323467329d8c4e97bc4932dd
Reviewed-on: https://gerrit.libreoffice.org/40222Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Tamás Zolnai <tamas.zolnai@collabora.com>