Fix incorrect subpath in links (#29535)

* `$referenceUrl`: it is constructed by "Issue.Link", which already has
the "AppSubURL"
* `window.location.href`: AppSubURL could be empty string, so it needs
the trailing slash

web_src/js/features/stopwatch.js

@@ -75,7 +75,7 @@ export function initStopwatch() {
           type: 'close',
         });
         worker.port.close();
-        window.location.href = appSubUrl;
+        window.location.href = `${appSubUrl}/`;
       } else if (event.data.type === 'close') {
         worker.port.postMessage({
           type: 'close',