asio: Add curly brackets to avoid possible well known issue

src/asio_server.cc

@@ -170,9 +170,9 @@ void server::start_accept(tcp::acceptor &acceptor, serve_mux &mux) {
           new_connection->start_read_deadline();
           new_connection->start();
         }
-        if (acceptor.is_open ())
+        if (acceptor.is_open()) {
           start_accept(acceptor, mux);
-
+        }
       });
 }