Coverity fix in apps/oscp

CID 1440002 (#1 of 1): Use after free (USE_AFTER_FREE)
Not a deadly error, because error was just before app exit.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7359)