enforce that DBG_UNHANDLED_EXCEPTION is called first in a catch block,
otherwise it cannot do it's job properly

Change-Id: I906436c6861212c44f8f21552ccbceb54f15c6e1
Reviewed-on: https://gerrit.libreoffice.org/52303Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>