message: guard against empty roomId/non-existant room
diff: @@ -424,7 +424,7 @@ module.exports = React.createClass({
  const cli = MatrixClientPeg.get();
  const room = cli.getRoom(this.props.roomId);
  let inviteButton;
  - if (room.getMyMembership() === 'join') {
  + if (room && room.getMyMembership() === 'join') {
  const TintableSvg = sdk.getComponent("elements.TintableSvg");
  const AccessibleButton = sdk.getComponent("elements.AccessibleButton");
  inviteButton =
  