Blank page when triggering OIDC logout while already logged out

### Describe the bug

Not sure if this is actually a bug or rather "desired" (but unexpected) behavior, but I observe the following phenomenon when using Authentik as an OIDC provider in web apps.

When logging out of an OIDC application while the user session in Authentik has already ended (for example, after previously logging out in another tab), the browser gets stuck on a completely blank white page with no content, error message, or redirection.

### How to reproduce

1. Log in to Authentik.
2. Open two separate browser tabs:
- Tab A: app 1 (e.g. custom internal app connected via OIDC)
- Tab B: app 2 (e.g. some third-party app such as Discourse, connected via OIDC)
3. In tab A, trigger logout -> Authentik post-logout screen is shown.
4. On the post-logout screen, click to log out completely -> redirected to the Authentik login screen.
5. Switch to tab B and trigger logout in app 2
6. A blank white page is rendered (HTTP `200 OK` with an empty response body). No redirect happens and no UI is displayed.

### Expected behavior

The user should either be redirected to the configured `post_logout_redirect_uri` / application or to the Authentik login screen.

### Screenshots

_No response_

### Additional context

_No response_

### Deployment Method

Docker

### Version

2026.8.0

### Relevant log output

```shell

```

No source file or test is named. Reproduce the two-tab logout sequence and trace the OIDC logout request that returns HTTP 200 with an empty body, then inspect the logout handling and its redirect decision. Done means an already-ended Authentik session redirects to the configured post_logout_redirect_uri or the Authentik login screen instead of rendering a blank page.

Written by the indexing model from the issue text.