Network: catch CircuitDestroyedException

This error is not catched because of removing generic try-with
and causes a red CI. In this commit we catch this error and
kill child circuits.

```
Unexpected exception happened in the retry loop, ex = System.AggregateException: One or more errors occurred. (Circuit got destroyed, reason ChannelClosed)
 ---> NOnion.CircuitDestroyedException: Circuit got destroyed, reason ChannelClosed
   --- End of inner exception stack trace ---
The active test run was aborted. Reason: Test host process crashed : Unhandled exception. System.AggregateException: One or more errors occurred. (Circuit got destroyed, reason ChannelClosed)
 ---> NOnion.CircuitDestroyedException: Circuit got destroyed, reason ChannelClosed
   --- End of inner exception stack trace ---
   at Microsoft.FSharp.Control.AsyncPrimitives.Start@907-1.Invoke(ExceptionDispatchInfo edi) in F:\workspace\_work\1\s\src\fsharp\FSharp.Core\async.fs:line 907
   at Microsoft.FSharp.Control.Trampoline.Execute(FSharpFunc`2 firstAction) in F:\workspace\_work\1\s\src\fsharp\FSharp.Core\async.fs:line 109
   at <StartupCode$FSharp-Core>.$Async.-ctor@163-1.Invoke(Object o) in F:\workspace\_work\1\s\src\fsharp\FSharp.Core\async.fs:line 165
   at System.Threading.QueueUserWorkItemCallback.Execute()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
```

NOnion/Network/TorGuard.fs

@@ -352,6 +352,10 @@ type TorGuard private (client: TcpClient, sslStream: SslStream) =
                                 self.HandleIncomingCellException<CircuitDecryptionFailedException>
                                     cell
                                     ex
+                            | :? CircuitDestroyedException as ex ->
+                                self.HandleIncomingCellException<CircuitDestroyedException>
+                                    cell
+                                    ex
                             | ex -> return raise <| FSharpUtil.ReRaise ex
                         | None ->
                             self.KillChildCircuits()