Do not create a session if accessing login page with a not supported browser #18560

When accessing the login page with a not supported browser like IE11, can we not create a session? This can prevent some issues where unneeded extra sessions are created. Seeing https://github.com/matomo-org/matomo/blob/4.6.2/core/FrontController.php#L426-L428 is checked after the session was created maybe? If easily doable, be great to move this check a wee bit further up before makeSessionAuthenticator so that when using an old browser, then no new entry in the session table is created.