Show an error message to the user when a direct link points to a non-existent session
For example: https://frag.jetzt/participant/room/11223345/comments
The session does not exist. The content area is empty. In this case, display an error saying:
We are sorry, but the session you want to join does not exist.
Please inform the person who gave you this direct link.
Use the snack bar component for the message and display it in red.