protected function _getProductQtyForCheck($productId, $itemQty)
 {
     if (!Mage::helper('udmulti')->isActive()) {
         return parent::_getProductQtyForCheck($productId, $itemQty);
     }
     $qty = $itemQty;
     $pidKey = $this->getUdropshipVendor() ? $this->getUdropshipVendor() . '-' . $productId : $productId;
     if (isset($this->_checkedProductsQty[$pidKey])) {
         $qty += $this->_checkedProductsQty[$pidKey];
     }
     $this->_checkedProductsQty[$pidKey] = $qty;
     return $qty;
 }