message: Add energy writing to MapViewState::save()
diff: @@ -88,6 +88,10 @@ void MapViewState::save(const std::string& filePath)
  turns->attribute("count", mTurnCount);
  root->linkEndChild(turns);
  + auto energy = new XmlElement("energy");
  + energy->attribute("energy", mEnergy);
  + root->linkEndChild(energy);
  +
  XmlElement* population = new XmlElement("population");
  population->attribute("morale", mCurrentMorale);
  population->attribute("prev_morale", mPreviousMorale);
  