message: fix flashing `by ""`
diff: @@ -29,7 +29,7 @@ const RedactedBody = React.forwardRef<any, IProps>(({mxEvent}, ref) => {
  let text = _t("Message deleted");
  const redactedBecauseUserId = mxEvent.getUnsigned().redacted_because.sender;
  - if (redactedBecauseUserId !== cli.getUserId()) {
  + if (redactedBecauseUserId && redactedBecauseUserId !== cli.getUserId()) {
  const room = cli.getRoom(mxEvent.getRoomId());
  const sender = room && room.getMember(redactedBecauseUserId);
  text = _t("Message deleted by %(name)s", { name: sender ? sender.name : redactedBecauseUserId });
  