#881 msdemo: added default value for input.Sorting in ProductAppService GetListPagedAsync

samples/MicroserviceDemo/modules/product/src/ProductManagement.Application/ProductManagement/ProductAppService.cs

@@ -28,7 +28,7 @@ namespace ProductManagement
             await NormalizeMaxResultCountAsync(input);
 
             var products = await _productRepository
-                .OrderBy(input.Sorting)
+                .OrderBy(input.Sorting ?? "Name")
                 .Skip(input.SkipCount)
                 .Take(input.MaxResultCount)
                 .ToListAsync();