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;