Remove duplicate check for ModelState validity

Two other minor questions:

- Why not move the check for whether the product exists to before attaching and saving? Would also remove the need for the try/catch around SaveChanges().
- Use Any() instead of Count() in the ProductExists method.

Author: corydeppen

grid/odata-v4-web-api-binding-wrappers/KendoUIMVC5/Controllers/ProductsController.cs

@@ -43,11 +43,6 @@ public IHttpActionResult Put([FromODataUri] int key, Product product)
                 return BadRequest(ModelState);
             }
 
-            if (!ModelState.IsValid)
-            {
-                return BadRequest(ModelState);
-            }
-
             if (key != product.ProductID)
             {
                 return BadRequest();