Fix wrong lock claimed in x509 dir lookup.

x509 store's objects cache can get corrupted when using dir lookup
method in multithreaded application. Claim x509 store's lock when
accessing objects cache.

CLA: trivial
Reviewed-by: NRichard Levitte <levitte@openssl.org>
Reviewed-by: NTomas Mraz <tmraz@fedoraproject.org>
Reviewed-by: NBernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
Reviewed-by: NShane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/9326)

(cherry picked from commit a161738a708b5e284a4714edc0c976606ea7cb26)

crypto/x509/by_dir.c

@@ -327,10 +327,10 @@ static int get_cert_by_subject(X509_LOOKUP *xl, X509_LOOKUP_TYPE type,
         /*
          * we have added it to the cache so now pull it out again
          */
-        CRYPTO_THREAD_write_lock(ctx->lock);
+        X509_STORE_lock(xl->store_ctx);
         j = sk_X509_OBJECT_find(xl->store_ctx->objs, &stmp);
         tmp = sk_X509_OBJECT_value(xl->store_ctx->objs, j);
-        CRYPTO_THREAD_unlock(ctx->lock);
+        X509_STORE_unlock(xl->store_ctx);
 
         /* If a CRL, update the last file suffix added for this */