After rate limit reached stop processing

Once a rate limit is reached the remaining rates should not be evaluated. This restores the behaviour that is described in the readme,  regarding stacked requests.

MvcThrottle/ThrottlingFilter.cs

@@ -163,6 +163,8 @@ public override void OnActionExecuting(ActionExecutingContext filterContext)
                                 string.Format(message, rateLimit, rateLimitPeriod),
                                 QuotaExceededResponseCode,
                                 requestId);
+
+                            return;
                         }
                     }
                 }