Server is in maintenance mode warning for server selection screen

[mahibi]

1. have server in maintenance mode
2. try to login on mobile

• screen with "Nextcloud talk not available (not installed or restricted by admin)" is shown.
• After a few seconds the man screen is shown again with "Talk app is not installed on the server you tried to authenticate against"

On both screens there should be a clearer message that maintenance mode is activated

[sowjanyakch]

@mahibi - I could not reproduce the issues. On server selection screen, it correctly shows that server is in maintenance mode and it's the same case with login.