Merge branch 'benaadams/negative-threads' into dev

src/Microsoft.AspNet.Server.Kestrel/ServerFactory.cs

@@ -55,6 +55,13 @@ namespace Microsoft.AspNet.Server.Kestrel
 
                 disposables.Push(engine);
 
+                if (information.ThreadCount < 0)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(information.ThreadCount), 
+                        information.ThreadCount, 
+                        "ThreadCount cannot be negative");
+                }
+
                 engine.Start(information.ThreadCount == 0 ? 1 : information.ThreadCount);
 
                 foreach (var address in information.Addresses)