message: Fix an exception thrown due to use of std::map::at()
diff: @@ -20,12 +20,14 @@ using ProductionTypeTable = std::map<ProductType, ProductionCost>;
  */
  const ProductionTypeTable PRODUCTION_TYPE_TABLE =
  {
  + { ProductType::PRODUCT_NONE, ProductionCost() },
  +
  { ProductType::PRODUCT_DIGGER, ProductionCost(5, 10, 5, 5, 2) },
  { ProductType::PRODUCT_DOZER, ProductionCost(5, 10, 5, 5, 2) },
  { ProductType::PRODUCT_EXPLORER, ProductionCost(5, 10, 5, 5, 2) },
  { ProductType::PRODUCT_MINER, ProductionCost(5, 10, 5, 5, 2) },
  { ProductType::PRODUCT_ROAD_MATERIALS, ProductionCost(2, 2, 5, 0, 0) },
  - { ProductType::PRODUCT_TRUCK, ProductionCost(5, 10, 5, 5, 2) },
  + { ProductType::PRODUCT_TRUCK, ProductionCost(2, 5, 2, 2, 0) },
  { ProductType::PRODUCT_MAINTENANCE_PARTS, ProductionCost(2, 2, 2, 1, 1) },
  @@ -40,7 +42,6 @@ const ProductionCost& productCost(ProductType productType)
  }
  -
  Factory::Factory(const std::string& name, const std::string& spritePath, StructureID id) :
  Structure(name, spritePath, StructureClass::Factory, id)
  {}
  