Multiplayer: Ensure monster hitpoints are calculated reproducable in quest/set-maps (#5958)

* Always use the same seed for generating set/quest maps

* Use setlvltype for loading quest/set-map (instead of leveltype)

* Ensure dungeon flags are reset when loading a quest/set-map

Source/diablo.cpp

@@ -2710,7 +2710,14 @@ void LoadGameLevel(bool firstflag, lvl_entry lvldir)
 		InitStores();
 		InitAutomapOnce();
 	}
-	SetRndSeed(glSeedTbl[currlevel]);
+	if (!setlevel) {
+		SetRndSeed(glSeedTbl[currlevel]);
+	} else {
+		// Maps are not randomly generated, but the monsters max hitpoints are.
+		// So we need to ensure that we have a stable seed when generating quest/set-maps.
+		// For this purpose we reuse the normal dungeon seeds.
+		SetRndSeed(glSeedTbl[static_cast<size_t>(setlvlnum)]);
+	}
 
 	if (leveltype == DTYPE_TOWN) {
 		SetupTownStores();

Source/levels/drlg_l1.cpp

@@ -1304,12 +1304,12 @@ void CreateL5Dungeon(uint32_t rseed, lvl_entry entry)
 
 void LoadPreL1Dungeon(const char *path)
 {
-	memset(dungeon, Dirt, sizeof(dungeon));
+	InitDungeonFlags();
 
 	auto dunData = LoadFileInMem<uint16_t>(path);
 	PlaceDunTiles(dunData.get(), { 0, 0 }, Floor);
 
-	if (leveltype == DTYPE_CATHEDRAL)
+	if (setlvltype == DTYPE_CATHEDRAL)
 		FillFloor();
 
 	memcpy(pdungeon, dungeon, sizeof(pdungeon));
@@ -1319,12 +1319,12 @@ void LoadL1Dungeon(const char *path, Point spawn)
 {
 	LoadDungeonBase(path, spawn, Floor, Dirt);
 
-	if (leveltype == DTYPE_CATHEDRAL)
+	if (setlvltype == DTYPE_CATHEDRAL)
 		FillFloor();
 
 	Pass3();
 
-	if (leveltype == DTYPE_CRYPT)
+	if (setlvltype == DTYPE_CRYPT)
 		AddCryptObjects(0, 0, MAXDUNX, MAXDUNY);
 	else
 		AddL1Objs(0, 0, MAXDUNX, MAXDUNY);