User not found when signed out

[JonasWanke]

Fixes the following error that occurred while nobody is signed in because we still tried to detect whether the user uses a demo account:

I/flutter ( 9440): 🐛  12:22:39.120: Retrieving initial deep link…
I/flutter ( 9440): 💡  12:22:39.140: Initial deep link: null
I/flutter ( 9440): 🐛  12:22:39.433: Running…
I/flutter ( 9440): 🐛  12:22:39.757: Navigator: didPush null → https://test.schul-cloud.org/login
I/flutter ( 9440): 💤  12:22:40.267: Network: GET https://api.test.schul-cloud.org/users/
I/flutter ( 9440): ⚠️  12:22:40.720: Network 401: GET https://api.test.schul-cloud.org/users/
I/flutter ( 9440):  └─ Error:
I/flutter ( 9440):     {
I/flutter ( 9440):       "name": "NotAuthenticated",
I/flutter ( 9440):       "message": "Not authenticated",
I/flutter ( 9440):       "code": 401,
I/flutter ( 9440):       "className": "not-authenticated",
I/flutter ( 9440):       "data": {
I/flutter ( 9440):         "requestId": "5f0c5213df7c25002b2014a5"
I/flutter ( 9440):       },
I/flutter ( 9440):       "errors": {}
I/flutter ( 9440):     }

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• Merge branch 'master' into fix/user-not-found-when-signed-out

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