message: Replace QuestionDialog with InfoDialog
  Display a default message if no room topic is present
diff: @@ -154,13 +154,12 @@ export const CommandMap = {
  const topicEvents = room.currentState.getStateEvents('m.room.topic', '');
  const topic = topicEvents.getContent().topic;
  - const topicHtml = linkifyString(sanitizeHtml(topic));
  + const topicHtml = topic ? linkifyString(sanitizeHtml(topic)) : _t('This room has no topic.');
  - const QuestionDialog = sdk.getComponent('dialogs.QuestionDialog');
  - Modal.createTrackedDialog('Slash Commands', 'Topic', QuestionDialog, {
  + const InfoDialog = sdk.getComponent('dialogs.InfoDialog');
  + Modal.createTrackedDialog('Slash Commands', 'Topic', InfoDialog, {
  title: room.name,
  description: <div dangerouslySetInnerHTML={{ __html: topicHtml }} />,
  - hasCancelButton: false,
  });
  return success();
  },
  