Merge pull request #201 from EasyAbp/jadyn/fix-default-inventory-provider-fallback

fix `EShopProductsOptions.DefaultInventoryProviderName` fall back

modules/EasyAbp.EShop.Products/src/EasyAbp.EShop.Products.Domain/EasyAbp/EShop/Products/Products/ProductInventoryProviderResolver.cs

@@ -56,7 +56,7 @@ public class ProductInventoryProviderResolver : IProductInventoryProviderResolve
         if (providerName.IsNullOrEmpty())
         {
             var options = ServiceProvider.GetRequiredService<IOptions<EShopProductsOptions>>();
-            providerName = options.Value.DefaultInventoryProviderName;
+            providerName = options.Value.DefaultInventoryProviderName ?? DefaultProductInventoryProvider.DefaultProductInventoryProviderName;
         }
 
         TryBuildNameToProviderTypeMapping();