NKAI: fix error message can not take away last stack

AI/Nullkiller/AIGateway.cpp

@@ -867,6 +867,19 @@ void AIGateway::pickBestCreatures(const CArmedInstance * destinationArmy, const
 
 	auto bestArmy = nullkiller->armyManager->getBestArmy(destinationArmy, destinationArmy, source);
 
+	for(auto army : armies)
+	{
+		// move first stack at first slot if empty to avoid can not take away last creature
+		if(!army->hasStackAtSlot(SlotID(0)) && army->stacksCount() > 0)
+		{
+			cb->mergeOrSwapStacks(
+				army,
+				army,
+				SlotID(0),
+				army->Slots().begin()->first);
+		}
+	}
+
 	//foreach best type -> iterate over slots in both armies and if it's the appropriate type, send it to the slot where it belongs
 	for(SlotID i = SlotID(0); i.validSlot(); i.advance(1)) //i-th strongest creature type will go to i-th slot
 	{

AI/Nullkiller/Analyzers/HeroManager.cpp

@@ -236,7 +236,7 @@ const CGHeroInstance * HeroManager::findWeakHeroToDismiss(uint64_t armyLimit) co
 
 	for(auto existingHero : myHeroes)
 	{
-		if(ai->isHeroLocked(existingHero) && ai->getHeroLockedReason(existingHero) == HeroLockedReason::DEFENCE
+		if(ai->getHeroLockedReason(existingHero) == HeroLockedReason::DEFENCE
 			|| existingHero->getArmyStrength() >armyLimit
 			|| getHeroRole(existingHero) == HeroRole::MAIN
 			|| existingHero->movementPointsRemaining()

AI/Nullkiller/Behaviors/GatherArmyBehavior.cpp

@@ -119,10 +119,11 @@ Goals::TGoalVec GatherArmyBehavior::deliverArmyToHero(const CGHeroInstance * her
 
 		HeroExchange heroExchange(hero, path);
 
-		float armyValue = (float)heroExchange.getReinforcementArmyStrength() / hero->getArmyStrength();
+		uint64_t armyValue = heroExchange.getReinforcementArmyStrength();
+		float armyRatio = (float)armyValue / hero->getArmyStrength();
 
 		// avoid transferring very small amount of army
-		if(armyValue < 0.1f && armyValue < 20000)
+		if((armyRatio < 0.1f && armyValue < 20000) || armyValue < 500)
 		{
 #if NKAI_TRACE_LEVEL >= 2
 			logAi->trace("Army value is too small.");