to be sure we can avoid decompressing/recompressing

Regression from https://cgit.freedesktop.org/libreoffice/core/commit/?id=76ec54e8c9f3580450bca85236a4f5af0c328588

Change-Id: Iacd7b2419ea85756f936b17f04c4e495d15e5b81
Reviewed-on: https://gerrit.libreoffice.org/30163Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>