As the OUString equivalent shows, it needs to check == 0. Commit
33ecd0d5c4 for some reason also
dropped the cheap checks (even from OUString) that OString has,
so add them.
Change-Id: I88e68b5ae10fd76c3c08b9b36d5abed0fad17bbf
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/130753
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
Tested-by: Jenkins