Unlock only when lock was successful

Unlock only when lock was successful

Addressing issue (#24517):
Updated the example in CRYPTO_THREAD_run_once.pod to reflect that an unlock call should not be made if a write_lock failed.
Updated BIO_lookup_ex in bio_addr.c and ossl_engine_table_select in eng_table.c to not call unlock if the lock failed.

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from https://github.com/openssl/openssl/pull/24779)