Admin audit is not properly logging unsetting of expiration date

How it was found

In relation to https://hackerone.com/reports/1177353

1. Enable the audit log
2. Share a file
3. Set and expiration date

So far all looks good in the log

4. Unset the the expiration date.
5. See a pretty useless log line

Impact

The audit log is used to get a full trail of the actions which is now incompletely. With possible important information. It seems to be also listed on https://portal.nextcloud.com/article/using-the-audit-log-44.html