Invalidated sessionId causes problems if already logged in

[viktorgullmark]

If the sessionId is invalidated for some reason, while a user is already logged in and using Exilence, several functions will crash and a restart is required to keep using the app.

This is caused from the "sessionIdProvided" bool being true, while the actual sessionId is not valid.

To get around this, we need to double-check that the sessionId is valid at certain times in the app; e.g when going to settings and when a snapshot is starting.