Core: Fix crash in ~ScriptMgr

Fixes: #854
Fixes: #918
Fixes: #917

src/server/game/Scripting/ScriptMgr.h

@@ -760,7 +760,7 @@ class ScriptMgr
     friend class ScriptObject;
 
     ScriptMgr();
-    ~ScriptMgr();
+    virtual ~ScriptMgr();
 
     uint32 _scriptCount;
 
@@ -775,6 +775,9 @@ class ScriptMgr
         void IncrementScriptCount() { ++_scriptCount; }
         uint32 GetScriptCount() const { return _scriptCount; }
 
+    public: /* Unloading */
+        void Unload();
+
     public: /* SpellScriptLoader */
 
         void CreateSpellScripts(uint32 spell_id, std::list<SpellScript*>& script_vector);