message: Add guard against potential nullptr for older savegames
diff: @@ -596,7 +596,9 @@ NAS2D::Xml::XmlElement* writeResearch(const ResearchTracker& tracker)
  void readResearch(NAS2D::Xml::XmlElement* element, ResearchTracker& tracker)
  {
  - const std::vector<std::string> researchList = NAS2D::split(element->attribute("completed"));
  + if (!element) { return; }
  +
  + const std::vector<std::string> researchList = NAS2D::split(element->attribute("completed_techs"));
  for (auto& item : researchList)
  {
  