message: use connection error to detect network problem
diff: @@ -273,9 +273,7 @@ class RoomViewStore extends Store {
  });
  let msg = err.message ? err.message : JSON.stringify(err);
  console.log("Failed to join room:", msg);
  - // XXX: We are relying on the error message returned by browsers here.
  - // This isn't great, but it does generalize the error being shown to users.
  - if (msg && msg.startsWith("CORS request rejected")) {
  + if (err.name === "ConnectionError") {
  msg = _t("There was an error joining the room");
  }
  if (err.errcode === 'M_INCOMPATIBLE_ROOM_VERSION') {
  