Better visiblity in ui when device config not present

Hi,

When a user is disabled or his device gets deleted, the client looses connectivity, as expected.
However from a client UI perspective, this is not really clear.
In the defguard client under locations, the state remains connected/active with a green status symbol.

In settings/log these entries are present: ```internal error: device config not present in response```
Only after 5 minutes a popup appears with the message
```The Location XXX has been disconnected, since we have detected that the server is not responding with any traffic for 300s. If this message keeps occurring, please contact your administrator and inform them about this fact.```

Is it possible to indicate this more clearly (upon connection) to the client, that the connection cannot be established?

Das Issue nennt keine Dateien oder Tests; beginne damit, den Locations-Status und die Verbindungsbehandlung des Clients rund um die gemeldete fehlende Gerätekonfiguration nachzuverfolgen. Erledigt ist die Aufgabe, wenn die UI klar anzeigt, dass der Standort getrennt ist, wenn der Server keine Gerätekonfiguration bereitstellt, statt einen grünen verbundenen Status beizubehalten.

Vom Indexierungsmodell aus dem Issue-Text verfasst.