Offer type code depends on discount reference being set

From #2619448-21: Cart Refresh check for discount price components causes Coupon removal

commerce_discount_percentage contains the following line

      $delta = $wrapper->commerce_discounts->count();
      $order->commerce_discounts[LANGUAGE_NONE][$delta]['target_id'] = $discount_wrapper->discount_id->value();

if you change it to

      $order->commerce_discounts[LANGUAGE_NONE][]['target_id'] = $discount_wrapper->discount_id->value();