Added comments about auth checks done before begin_request()

mongoose.c

@@ -4202,6 +4202,8 @@ static void handle_request(struct mg_connection *conn) {
                                 get_remote_ip(conn), ri->uri);
 
   DEBUG_TRACE(("%s", ri->uri));
+  // Perform redirect and auth checks before calling begin_request() handler.
+  // Otherwise, begin_request() would need to perform auth checks and redirects.
   if (!conn->client.is_ssl && conn->client.ssl_redir &&
       (ssl_index = get_first_ssl_listener_index(conn->ctx)) > -1) {
     redirect_to_https_port(conn, ssl_index);