Fix the mem_sec "small arena"

Fix the small arena test to just check for the symptom of the infinite
loop (i.e. initialized set on failure), rather than the actual infinite
loop. This avoids some valgrind errors.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Andy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3512)