Add seed validation for server world creation and override-seed property

The dedicated server previously picked a completely random seed with no
biome diversity checks (the client validates but the server skipped it).
On top of that, the client's findSeed() was hardcoded to only check a
54-chunk (Classic) area, so Large worlds had no diversity guarantee
beyond the center.

New server worlds now use findSeed() scaled to the full target world
size. Added override-seed in server.properties to fix existing worlds
without deleting them.

Minecraft.Client/Common/Consoles_App.cpp

@@ -206,6 +206,8 @@ CMinecraftApp::CMinecraftApp()
 	m_dwRequiredTexturePackID=0;
 
 	m_bResetNether=false;
+	m_seedOverride = 0;
+	m_hasSeedOverride = false;
 
 #ifdef _XBOX
 	//	m_bTransferSavesToXboxOne=false;

Minecraft.Client/Common/Consoles_App.h

@@ -706,6 +706,8 @@ private:
 	bool			m_bGameNewWorldSizeUseMoat;
 	unsigned int	m_GameNewHellScale;
 #endif
+	int64_t			m_seedOverride;
+	bool			m_hasSeedOverride;
 	unsigned int	FromBigEndian(unsigned int uiValue);
 
 public:
@@ -723,6 +725,10 @@ public:
 	void			SetGameNewHellScale(unsigned int newScale)				{ m_GameNewHellScale = newScale; }
 	unsigned int	GetGameNewHellScale()									{ return m_GameNewHellScale; }
 #endif
+	void			SetSeedOverride(int64_t seed)	{ m_seedOverride = seed; m_hasSeedOverride = true; }
+	bool			HasSeedOverride()				{ return m_hasSeedOverride; }
+	int64_t			GetSeedOverride()				{ return m_seedOverride; }
+
 	void			SetResetNether(bool bResetNether) {m_bResetNether=bResetNether;}
 	bool			GetResetNether() {return m_bResetNether;}
 	bool			CanRecordStatsAndAchievements();

Minecraft.Client/MinecraftServer.cpp

@@ -735,10 +735,11 @@ bool MinecraftServer::initServer(int64_t seed, NetworkGameInitData *initData, DW
 
 	if( findSeed )
 	{
+		int worldSizeChunks = (initData && initData->xzSize > 0) ? (int)initData->xzSize : 54;
 #ifdef __PSVITA__
-		seed = BiomeSource::findSeed(pLevelType, &running);
+		seed = BiomeSource::findSeed(pLevelType, &running, worldSizeChunks);
 #else
-		seed = BiomeSource::findSeed(pLevelType);
+		seed = BiomeSource::findSeed(pLevelType, worldSizeChunks);
 #endif
 	}