Garrisoning behavior improvement

AI will now also garrison a hero as defender if the town to be defended has troops as long as the hero can merge their own troops with the town.

AI will no longer just dismiss existing troops in a town if a hero trying to garrison there can merge with it.

AI/Nullkiller/Behaviors/DefenceBehavior.cpp

@@ -270,6 +270,7 @@ void DefenceBehavior::evaluateDefence(Goals::TGoalVec & tasks, const CGTownInsta
 				// dismiss creatures we are not able to pick to be able to hide in garrison
 				if(town->garrisonHero
 					|| town->getUpperArmy()->stacksCount() == 0
+					|| path.targetHero->canBeMergedWith(*town)
 					|| (town->getUpperArmy()->getArmyStrength() < 500 && town->fortLevel() >= CGTownInstance::CITADEL))
 				{
 					tasks.push_back(

AI/Nullkiller/Goals/ExchangeSwapTownHeroes.cpp

@@ -90,9 +90,12 @@ void ExchangeSwapTownHeroes::accept(AIGateway * ai)
 	
 	if(!town->garrisonHero)
 	{
-		while(upperArmy->stacksCount() != 0)
+		if (!garrisonHero->canBeMergedWith(*town))
 		{
-			cb->dismissCreature(upperArmy, upperArmy->Slots().begin()->first);
+			while (upperArmy->stacksCount() != 0)
+			{
+				cb->dismissCreature(upperArmy, upperArmy->Slots().begin()->first);
+			}
 		}
 	}