Add missing log_event when application uses its own record layer

This commit adds missing log_event callback invocation when an
application uses its own record layer.  While such application may use
update_traffic_key callback to log secrets, it still be useful to
share log_event callback with a regular TLS application.
diff --git a/lib/picotls.c b/lib/picotls.c
index b12a12c..2ab6e9c 100644
--- a/lib/picotls.c
+++ b/lib/picotls.c
@@ -1636,6 +1636,8 @@
 
     /* special path for applications having their own record layer */
     if (tls->ctx->update_traffic_key != NULL) {
+        log_secret(tls, log_labels[ptls_is_server(tls) == is_enc][epoch],
+                   ptls_iovec_init(ctx->secret, tls->key_schedule->hashes[0].algo->digest_size));
         if (skip_notify)
             return 0;
         return tls->ctx->update_traffic_key->cb(tls->ctx->update_traffic_key, tls, is_enc, epoch, ctx->secret);