Core/Cleanup: remove C-style cast to (Bag*):

* add ToBag() methods for Item class;
* add GetBagByPos() method for Player class.

src/server/game/Entities/Item/Item.cpp

@@ -281,6 +281,15 @@ bool Item::Create(uint32 guidlow, uint32 itemid, Player const* owner)
     return true;
 }
 
+// Returns true if Item is a bag AND it is not empty.
+// Returns false if Item is not a bag OR it is an empty bag.
+bool Item::IsNotEmptyBag() const
+{
+    if (const Bag* pBag = ToBag())
+        return !pBag->IsEmpty();
+    return false;
+}
+
 void Item::UpdateDuration(Player* owner, uint32 diff)
 {
     if (!GetUInt32Value(ITEM_FIELD_DURATION))

src/server/game/Entities/Item/Item.h

@@ -253,8 +253,12 @@ class Item : public Object
         void SaveRefundDataToDB();
         void DeleteRefundDataFromDB();
 
+        Bag* ToBag() { if (IsBag()) return reinterpret_cast<Bag*>(this); else return NULL; }
+        const Bag* ToBag() const { if (IsBag()) return reinterpret_cast<const Bag*>(this); else return NULL; }
+
         bool IsLocked() const { return !HasFlag(ITEM_FIELD_FLAGS, ITEM_FLAG_UNLOCKED); }
         bool IsBag() const { return GetProto()->InventoryType == INVTYPE_BAG; }
+        bool IsNotEmptyBag() const;
         bool IsBroken() const { return GetUInt32Value(ITEM_FIELD_MAXDURABILITY) > 0 && GetUInt32Value(ITEM_FIELD_DURABILITY) == 0; }
         bool CanBeTraded(bool mail = false, bool trade = false) const;
         void SetInTrade(bool b = true) { mb_in_trade = b; }