AK1001: must close over Sender when using PipeTo

[Aaronontheweb]

Changes

Not 100% sure that this is an issue in newer versions of Akka.NET, but it's still a good idea to enforce this.

Should flag the following code:

using Akka.Actor;

public sealed class MyActor : ReceiveActor{
    Receive<string>(str => {
         async Task<int> LocalFunction(){
              await Task.Delay(10);
              return str.Length;
         }

         // invoke detatched async Task and PipeTo sender
         LocalFunction().PipeTo(Sender); // BUG: need to close over this.Sender using a local variable, because that value can change by the time the async function finishes evaluating.
     });
}