Core/Instances: Fix memory leak in InstanceSaveMgr

Fix memory leak in InstanceSaveMgr added in 1f170c99ef .
Make InstanceSave::SetToDelete() private since it's not supposed to be used by anything other than InstanceSave or its friend class InstanceSaveMgr .

Closes #82

src/server/game/Instances/InstanceSaveMgr.cpp

@@ -169,7 +169,11 @@ void InstanceSaveManager::RemoveInstanceSave(uint32 InstanceId)
 void InstanceSaveManager::UnloadInstanceSave(uint32 InstanceId)
 {
     if (InstanceSave* save = GetInstanceSave(InstanceId))
+    {
         save->UnloadIfEmpty();
+        if (save->m_toDelete)
+            delete save;
+    }
 }
 
 InstanceSave::InstanceSave(uint16 MapId, uint32 InstanceId, Difficulty difficulty, time_t resetTime, bool canReset)

src/server/game/Instances/InstanceSaveMgr.h

@@ -120,16 +120,16 @@ class InstanceSave
            but that would depend on a lot of things that can easily change in future */
         Difficulty GetDifficulty() const { return m_difficulty; }
 
+        typedef std::list<Player*> PlayerListType;
+        typedef std::list<Group*> GroupListType;
+    private:
+        bool UnloadIfEmpty();
         /* used to flag the InstanceSave as to be deleted, so the caller can delete it */
         void SetToDelete(bool toDelete)
         {
             m_toDelete = toDelete;
         }
 
-        typedef std::list<Player*> PlayerListType;
-        typedef std::list<Group*> GroupListType;
-    private:
-        bool UnloadIfEmpty();
         /* the only reason the instSave-object links are kept is because
            the object-instSave links need to be broken at reset time */
            /// @todo: Check if maybe it's enough to just store the number of players/groups