:lady_beetle: bug: exporting attendee information with no events results in `KeyError`

[sentry-io[bot]]

Sentry Issue: INDOKWEB-BACKEND-12

KeyError: "None of ['id'] are in the columns"
(2 additional frame(s) were not displayed)
...
  File "graphql/execution/middleware.py", line 75, in make_it_promise
    return next(*args, **kwargs)
  File "apps/events/resolvers.py", line 128, in resolve_attendee_report_org
    df = create_attendee_report(event_ids, fields)
  File "apps/events/resolvers.py", line 148, in create_attendee_report
    df_events = pd.DataFrame(Event.objects.filter(id__in=event_ids).values()).set_index("id").add_prefix("event_")
  File "pandas/util/_decorators.py", line 311, in wrapper
    return func(*args, **kwargs)
  File "pandas/core/frame.py", line 5446, in set_index
    raise KeyError(f"None of {missing} are in the columns")