item_generic: add missing Save/Restore method declarations inside the class

src/gs-entbase/server/item_generic.qc

@@ -37,6 +37,8 @@ public:
 
 	virtual void Respawn(void);
 	virtual void SpawnKey(string, string);
+	virtual void Save(float);
+	virtual void Restore(string, string);
 private:
 	string m_strSequenceName;
 };