iMIP error invisible to user

[ChristophWurst]

Steps to reproduce

1. Respond to an iMIP invitation
2. ???

Expected behavior

As a user the system tells me that something went wrong. I therefore know that my attendance wasn't save or sent back to the organizer.

Actual behavior

It looks like everything worked as expected.

https://github.com/nextcloud/mail/pull/6956#discussion_r958554117

Mail app version

2.0.0 beta 4

Mailserver or service

No response

Operating system

No response

PHP engine version

No response

Web server

No response

Database

No response

Additional info

No response