message: Re-initialize Population rather than call .clear()
  This may actually do a better job of clearing, since the .clear() method
  only actually resets one internal field.
diff: @@ -532,7 +532,7 @@ void MapViewState::readPopulation(Xml::XmlElement* element)
  {
  if (element)
  {
  - mPopulation.clear();
  + mPopulation = {};
  const auto dictionary = NAS2D::attributesToDictionary(*element);
  