get certificate info only for debug build

src/event/ngx_event_openssl.c

diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index a2304ef..559c007 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -285,6 +285,7 @@
 static int
 ngx_http_ssl_verify_callback(int ok, X509_STORE_CTX *x509_store)
 {
+#if (NGX_DEBUG)
     char              *subject, *issuer;
     int                err, depth;
     X509              *cert;
@@ -319,6 +320,7 @@
     if (iname) {
         OPENSSL_free(issuer);
     }
+#endif
 
     return 1;
 }