message: Fixes unintentional bug when MoraleModifier is given negative numbers
  It also has no reason to be a full class, a POD struct is fine.
diff: /**
  * Morale modifier values.
  */
  -class MoraleModifier
  +struct MoraleModifier
  {
  public:
  - MoraleModifier(uint32_t rBonus, uint32_t pBonus, uint32_t fRate, uint32_t mRate) :
  + MoraleModifier() = default;
  + MoraleModifier(int rBonus, int pBonus, int fRate, int mRate) :
  researchBonus(rBonus), productionBonus(pBonus), fertilityRate(fRate), mortalityRate(mRate)
  {}
  - MoraleModifier() : researchBonus(0), productionBonus(0), fertilityRate(0), mortalityRate(0)
  - {}
  -
  -public:
  - int researchBonus;
  - int productionBonus;
  - int fertilityRate;
  - int mortalityRate;
  + int researchBonus{0};
  + int productionBonus{0};
  + int fertilityRate{0};
  + int mortalityRate{0};
  };
  