message: Load mine veins positionally
  The `id` field is really just a positional index, but that is preserved
  when writing and reading the data anyway, so isn't really needed.
diff: @@ -337,7 +337,8 @@ void Mine::deserialize(NAS2D::Xml::XmlElement* element)
  this->active(active);
  mProductionRate = static_cast<MineProductionRate>(yield);
  - mVeins.resize(static_cast<std::size_t>(depth));
  + mVeins.resize(0);
  + mVeins.reserve(static_cast<std::size_t>(depth));
  for (auto* vein = element->firstChildElement(); vein != nullptr; vein = vein->nextSiblingElement())
  {
  const auto veinDictionary = NAS2D::attributesToDictionary(*vein);
  @@ -347,8 +348,7 @@ void Mine::deserialize(NAS2D::Xml::XmlElement* element)
  mineVein[OreType::ORE_COMMON_MINERALS] = veinDictionary.get<int>("common_minerals");
  mineVein[OreType::ORE_RARE_METALS] = veinDictionary.get<int>("rare_metals");
  mineVein[OreType::ORE_RARE_MINERALS] = veinDictionary.get<int>("rare_minerals");
  - const auto id = veinDictionary.get<int>("id");
  - mVeins[static_cast<std::size_t>(id)] = mineVein;
  + mVeins.push_back(mineVein);
  }
  }
  