U4-8103 - fix DisableBrowserCacheAttribute to handle exceptions

src/Umbraco.Web/WebApi/Filters/DisableBrowserCacheAttribute.cs

@@ -1,15 +1,6 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Net.Http;
 using System.Net.Http.Headers;
-using System.Text;
-using System.Threading;
-using System.Threading.Tasks;
-using System.Web;
-using System.Web.Http.Controllers;
 using System.Web.Http.Filters;
-using Umbraco.Core;
 
 namespace Umbraco.Web.WebApi.Filters
 {
@@ -24,6 +15,9 @@ namespace Umbraco.Web.WebApi.Filters
 
             base.OnActionExecuted(actionExecutedContext);
 
+            // happens if exception
+            if (actionExecutedContext.Response == null) return;
+
             //NOTE: Until we upgraded to WebApi 2, this didn't work correctly and we had to revert to using
             // HttpContext.Current responses. I've changed this back to what it should be now since it works
             // and now with WebApi2, the HttpContext.Current responses dont! Anyways, all good now.
@@ -42,9 +36,6 @@ namespace Umbraco.Web.WebApi.Filters
                     //Mon, 01 Jan 1990 00:00:00 GMT
                     new DateTimeOffset(1990, 1, 1, 0, 0, 0, TimeSpan.Zero);
             }
-
-            
-            
         }
     }
 }