message: size header explicitly for content size
  otherwise it just grows with max-height
diff: @@ -65,8 +65,9 @@ class RoomDistributor {
  _contentSize(item) {
  const scrollItem = item.domNode.querySelector(".mx_RoomSubList_scroll");
  - const headerHeight = item.size() - scrollItem.offsetHeight;
  - return headerHeight + scrollItem.scrollHeight + 4;
  + const header = item.domNode.querySelector(".mx_RoomSubList_labelContainer");
  + const headerHeight = item.sizer.getItemSize(header);
  + return headerHeight + scrollItem.scrollHeight;
  }
  resize(size) {
  