message: RoomView: guard against unmounting during peeking
  it's possible for the user to change room before the peek operation completes. Check if we've been unmounted before setting state.
diff: @@ -264,12 +264,19 @@ module.exports = React.createClass({
  isPeeking: true, // this will change to false if peeking fails
  });
  MatrixClientPeg.get().peekInRoom(roomId).then((room) => {
  + if (this.unmounted) {
  + return;
  + }
  this.setState({
  room: room,
  peekLoading: false,
  });
  this._onRoomLoaded(room);
  }, (err) => {
  + if (this.unmounted) {
  + return;
  + }
  +
  // Stop peeking if anything went wrong
  this.setState({
  isPeeking: false,
  @@ -286,7 +293,7 @@ module.exports = React.createClass({
  } else {
  throw err;
  }
  - }).done();
  + });
  }
  } else if (room) {
  // Stop peeking because we have joined this room previously
  