message: Throw an error when the MorphableModel version being loaded is neither 1, 2, 3 or 4
  The error is also different from the error when a model of version <1 is loaded.
  This might help diagnose problems like
diff: @@ -482,7 +482,8 @@ private:
  *
  * @param[in] archive The archive to serialise to (or to serialise from).
  * @param[in] version Version number of the archive.
  - * @throw std::runtime_error When the model file doesn't have the most recent version (=1).
  + * @throw std::runtime_error When the model file has version <1 (the very old cv::Mat matrix format) or an
  + * unknown value (e.g. >4).
  */
  template <class Archive>
  void serialize(Archive& archive, const std::uint32_t version)
  @@ -503,11 +504,15 @@ private:
  {
  archive(CEREAL_NVP(shape_model), CEREAL_NVP(color_model), CEREAL_NVP(expression_model),
  CEREAL_NVP(landmark_definitions), CEREAL_NVP(texture_coordinates));
  - } else
  + } else if (version == 4)
  {
  archive(CEREAL_NVP(shape_model), CEREAL_NVP(color_model), CEREAL_NVP(expression_model),
  CEREAL_NVP(landmark_definitions), CEREAL_NVP(texture_coordinates),
  CEREAL_NVP(texture_triangle_indices));
  + } else
  + {
  + throw std::runtime_error("The model file you are trying to load has an unknown version number: " +
  + std::to_string(version));
  }
  };
  };
  