Ensure that when SSS omits heroes we don't forget we had heroes

Otherwise when the room next appears the name/avatar reset to
'Empty Room' with no avatar.

src/models/room.ts

@@ -1672,7 +1672,7 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
  if (Number.isInteger(invitedCount)) {
  this.currentState.setInvitedMemberCount(invitedCount!);
  }
- if (Array.isArray(heroes)) {
+ if (Array.isArray(heroes) && heroes.length > 0) {
  // filter out ourselves just in case
  this.heroes = heroes.filter((h) => {
  return h.userId != this.myUserId;