We need to ask the NWF for the size of the thumb and not just use
the hard-coded value.

Reviewed-on: https://gerrit.libreoffice.org/70201
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
(cherry picked from commit 9956cf06)

Change-Id: I98c6b5782c6a043fc358198ddf844d36d7aa90d6