Fix reloading NC after logging out from IDP

[LEDfan]

Related to #345 Using: Nextcloud master (17) user_saml master and keycloak 4.8.3.Final.

Steps to reproduce:

1. Login on Nextcloud using Keycloak
2. Go to the account settings of Keycloak e.g. https://idp/auth/realms/my-realm/account/
3. Click the logout button
4. Reload an existing tab

Expected

After the #334 and #340 it is expected to be logged out and redirected to the login page of the SSO again.

Actual Result

You get a redirect loop:

The third request doesn't have a valid CRSF token and fails.