message: show error if we can't set a filter
  this way it still works for a room we've been in before
diff: @@ -59,6 +59,8 @@ var FilePanel = React.createClass({
  var client = MatrixClientPeg.get();
  var room = client.getRoom(roomId);
  + this.noRoom = !room;
  +
  if (room) {
  var filter = new Matrix.Filter(client.credentials.userId);
  filter.setDefinition(
  @@ -82,13 +84,18 @@ var FilePanel = React.createClass({
  console.error("Failed to get or create file panel filter", error);
  }
  );
  - }
  - else {
  + } else {
  console.error("Failed to add filtered timelineSet for FilePanel as no room!");
  }
  },
  render: function() {
  + if (this.noRoom) {
  + return <div className="mx_FilePanel mx_RoomView_messageListWrapper">
  + <div className="mx_RoomView_empty">You must join the room to see its files</div>
  + </div>;
  + }
  +
  // wrap a TimelinePanel with the jump-to-event bits turned off.
  var TimelinePanel = sdk.getComponent("structures.TimelinePanel");
  var Loader = sdk.getComponent("elements.Spinner");
  