Fix bug with tier pricing

Author: tatarincev

STOREFRONT/VirtoCommerce.Storefront.Model/Catalog/Product.cs

@@ -253,7 +253,7 @@ public void ApplyPrices(IEnumerable<ProductPrice> prices, Currency currentCurren
                 var orderedPrices = currencyGroup.OrderBy(x => x.MinQuantity ?? 0).ThenBy(x => x.ListPrice);
                 var nominalPrice = orderedPrices.FirstOrDefault();
                 //and add to nominal price other prices as tier prices
-                nominalPrice.TierPrices.AddRange(orderedPrices.Select(x => new TierPrice(x.SalePrice, x.MinQuantity ?? 0)));
+                nominalPrice.TierPrices.AddRange(orderedPrices.Select(x => new TierPrice(x.SalePrice, x.MinQuantity ?? 1)));
                 //Add nominal price to product prices list 
                 Prices.Add(nominalPrice);
             }
@@ -268,6 +268,7 @@ public void ApplyPrices(IEnumerable<ProductPrice> prices, Currency currentCurren
                     if (Prices.Any())
                     {
                         price = Prices.First().ConvertTo(currency);
+                        price.TierPrices.Add(new TierPrice(price.SalePrice, 1));
                     }
                     Prices.Add(price);
                 }

STOREFRONT/VirtoCommerce.Storefront.Model/Catalog/ProductPrice.cs

@@ -112,7 +112,11 @@ public Money ActualPrice
         /// <returns></returns>
         public TierPrice GetTierPrice(int quantity)
         {
-            var retVal = TierPrices.OrderBy(x => x.Quantity).Last(x => x.Quantity <= quantity);
+            var retVal = TierPrices.OrderBy(x => x.Quantity).LastOrDefault(x => x.Quantity <= quantity);
+            if(retVal == null)
+            {
+                retVal = new TierPrice(SalePrice, 1);
+            }
             return retVal;
         }