apps/lib/apps.c: Add a check for OPENSSL_strdup()

apps/lib/apps.c: Add a check for OPENSSL_strdup()

Add a check for the return value of OPENSSL_strdup() to guarantee the success of allocation, similar to the other call sites.

Fixes: c7d5ea2670 ("Prepare to detect index changes in OCSP responder.")
Signed-off-by: JiashengJiang <jiasheng@purdue.edu>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/27172)