message: EventIndex: Handle invalid m.room.redaction events correctly.
  Clients might send invalid redaction events, such events will not have a
  valid redacts field containing the event id of the associated event that
  was redacted.
  Skip such events instead of ending up looping over the checkpoint
  forever.
diff: @@ -507,7 +507,14 @@ export default class EventIndex extends EventEmitter {
  try {
  for (let i = 0; i < redactionEvents.length; i++) {
  const ev = redactionEvents[i];
  - await indexManager.deleteEvent(ev.getAssociatedId());
  + const eventId = ev.getAssociatedId();
  +
  + if (eventId) {
  + await indexManager.deleteEvent(eventId);
  + } else {
  + console.log("EventIndex: Redaction event doesn't contain a",
  + "valid associated event id", ev);
  + }
  }
  const eventsAlreadyAdded = await indexManager.addHistoricEvents(
  