It seems to me we should:
- Adjust the catch in https://git.kolab.org/diffusion/RPK/browse/master/plugins/libcalendaring/lib/libcalendaring_vcalendar.php (to specifically just ignore a broken itip).
- Adjust all the catches in Sync.php to also catch Throwable
- Add a test that triggers this error to the syncroton testsuite
- Remove the catch in this patch again, so we don't end up with 3 layers potentially catching.
..