apps/ocsp.c: Add missing test if make_ocsp_response failed

CLA: trivial

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19660)

(cherry picked from commit 93e1271e)