fix: session not persisting to database in some scenarios

In some edge cases (e.g. SSO plugin redirecting the user immediately), with modern browsers, the request is never "completed" for speed. This causes a condition where the session object never persists to the database, even though it has changed. This added line forces a db persist on a successful login.

Context: expressjs/session#484

src/controllers/authentication.js

@@ -352,6 +352,7 @@ authenticationController.onSuccessfulLogin = async function (req, uid) {
 			version: req.useragent.version,
 		});
 		await Promise.all([
+			new Promise(resolve => req.session.save(resolve)),
 			user.auth.addSession(uid, req.sessionID),
 			user.updateLastOnlineTime(uid),
 			user.updateOnlineUsers(uid),