This is partially based on the report and patch from
Jason Volk <jason@zemos.net>, however it actually fixes the issue
properly in both cases and doesn't rethrow the callbacks own exception
for error handling... It also improves the error message for aborted
callbacks by hardcoding the curl error code. This regularly happens when
you close Nheko and it cancels the sync request.

It makes no sense for servers to send the parent object without events
and not sending an empty list, but strictly speaking that is spec
compliant, so...

Relates to https://github.com/Nheko-Reborn/nheko/issues/1257

* Add confetti support

fixes https://github.com/Nheko-Reborn/nheko/issues/1218

See https://github.com/matrix-org/synapse/issues/13375