Update mapgen params in ServerMap after Mapgen init

src/map.h

@@ -496,6 +496,7 @@ public:
 	u64 getSeed(){ return m_seed; }
 
 	MapgenParams *getMapgenParams(){ return m_mgparams; }
+	void setMapgenParams(MapgenParams *mgparams){ m_mgparams = mgparams; }
 
 	// Parameters fed to the Mapgen
 	MapgenParams *m_mgparams;