using autorelease here leads to “just leaking” because there's no autorelease pool for thread
besides, make sure that released fields do not contain used•to•be•a•valid•pointer value

Change-Id: Id6cb37643230f64dbe9f6128f52236f04d0c88e4
Reviewed-on: https://gerrit.libreoffice.org/22981Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>