In addition, create a meaningful error message and don't create and
artificial error message if there exists a custom one.
Change-Id: I682e497ee3fdfe4da80fb17ab41c1b4cf90eb2cb
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/122206
Tested-by: Jenkins
Reviewed-by: Andreas Heinisch <andreas.heinisch@yahoo.de>
