... file format by default if the requested filter does not exist.

Much better to write an error message and do nothing.

Change-Id: Ie5404772e7aae5751126bd4c2784b58177804448
(cherry picked from commit c994ce8a)
Reviewed-on: https://gerrit.libreoffice.org/20007Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>
(cherry picked from commit de7a50d6)