fix: Spawn Monsters memory leak (#538)

This PR fixes memory leak issues in spawn monsters.

Author: jprzimba

src/creatures/monsters/spawns/spawn_monster.cpp

@@ -129,10 +129,18 @@ bool SpawnsMonster::loadFromXML(const std::string &filemonstername) {
 }
 
 void SpawnsMonster::startup() {
-	if (!isLoaded() || isStarted()) {
+	if (!isLoaded()) {
 		return;
 	}
 
+	if (isStarted()) {
+		for (const auto &spawnMonster : spawnMonsterList) {
+			spawnMonster->stopEvent();
+			spawnMonster->removeMonsters();
+		}
+		started = false;
+	}
+
 	for (const auto &spawnMonster : spawnMonsterList) {
 		spawnMonster->startup();
 	}
@@ -143,6 +151,7 @@ void SpawnsMonster::startup() {
 void SpawnsMonster::clear() {
 	for (const auto &spawnMonster : spawnMonsterList) {
 		spawnMonster->stopEvent();
+		spawnMonster->removeMonsters();
 	}
 	spawnMonsterList.clear();
 
@@ -181,6 +190,7 @@ void SpawnMonster::startSpawnMonsterCheck() {
 
 SpawnMonster::~SpawnMonster() {
 	stopEvent();
+	removeMonsters();
 }
 
 // moveable
@@ -336,6 +346,9 @@ void SpawnMonster::cleanup() {
 	for (auto it = spawnedMonsterMap.begin(); it != spawnedMonsterMap.end();) {
 		const auto &monster = it->second;
 		if (!monster || monster->isRemoved()) {
+			if (monster) {
+				monster->setSpawnMonster(nullptr);
+			}
 			auto spawnIt = spawnMonsterMap.find(it->first);
 			if (spawnIt != spawnMonsterMap.end()) {
 				spawnIt->second.lastSpawn = OTSYS_TIME();
@@ -425,10 +438,20 @@ void SpawnMonster::removeMonster(const std::shared_ptr<Monster> &monster) {
 			break;
 		}
 	}
-	spawnedMonsterMap.erase(spawnMonsterId);
+	if (spawnMonsterId != 0) {
+		if (monster) {
+			monster->setSpawnMonster(nullptr);
+		}
+		spawnedMonsterMap.erase(spawnMonsterId);
+	}
 }
 
 void SpawnMonster::removeMonsters() {
+	for (auto &[id, monster] : spawnedMonsterMap) {
+		if (monster) {
+			monster->setSpawnMonster(nullptr);
+		}
+	}
 	spawnMonsterMap.clear();
 	spawnedMonsterMap.clear();
 }