message: Throw runtime exception if pointer to structure is null inside StructureInspector
diff: #include <map>
  #include <sstream>
  +#include <stdexcept>
  using namespace NAS2D;
  @@ -134,8 +135,7 @@ void StructureInspector::update()
  if (mStructure == nullptr)
  {
  - text("NULLPTR!");
  - return;
  + throw std::runtime_error("Null pointer to structure within StructureInspector");
  }
  text(mStructure->name());
  