[CAL-4389] Errors on existing bookings that have previously connected calendar connections

[emrysal]

Issue Summary

Existing bookings on disconnected or broken calendar integrations throw various errors on modification or deletion. Improving the situation is paramount.

Steps to Reproduce

1. Connect a Calendar, such as Google Calendar
2. Create a event, such as a seated event or recurring event.
3. Book the event
4. Make a change to the booking, such as booking an additional seat - the error shows up.

Optional

5. Re-connect the same calendar
6. Retry (4.)
7. Note that the error still shows up, there is no recovery.

Any other relevant information. For example, why do you consider this a bug and what did you expect to happen instead?

Evidence

_{From SyncLinear.com | CAL-4389}