message: Make missing rooms throw instead
  For now at least. We shouldn't encounter this case until we get around to adding support for newly-joined rooms.
diff: @@ -207,15 +207,12 @@ export class ImportanceAlgorithm extends Algorithm {
  const taggedRooms = this.cached[tag];
  const indicies = this.indices[tag];
  let roomIdx = taggedRooms.indexOf(room);
  - let inList = true;
  if (roomIdx === -1) {
  console.warn(`Degrading performance to find missing room in "${tag}": ${room.roomId}`);
  roomIdx = taggedRooms.findIndex(r => r.roomId === room.roomId);
  }
  if (roomIdx === -1) {
  - console.warn(`Room ${room.roomId} has no index in ${tag} - assuming end of list`);
  - roomIdx = taggedRooms.length;
  - inList = false; // used so we don't splice the dead room out
  + throw new Error(`Room ${room.roomId} has no index in ${tag}`);
  }
  // Try to avoid doing array operations if we don't have to: only move rooms within
  