Improve disposal logic in AsyncWebsocketMessageResultEnumerator to prevent multiple disposals (#476)

* Improve disposal logic in AsyncWebsocketMessageResultEnumerator to prevent multiple disposals

* fb

* Update src/Custom/RealtimeConversation/Internal/AsyncWebsocketMessageEnumerator.cs

Co-authored-by: Stephen Toub <[email protected]>

---------

Co-authored-by: Stephen Toub <[email protected]>

Author: christothes

src/Custom/RealtimeConversation/Internal/AsyncWebsocketMessageEnumerator.cs

@@ -13,7 +13,7 @@ internal partial class AsyncWebsocketMessageResultEnumerator : IAsyncEnumerator<
     public ClientResult Current { get; private set; }
     private readonly CancellationToken _cancellationToken;
     private readonly WebSocket _webSocket;
-    private readonly byte[] _receiveBuffer;
+    private byte[] _receiveBuffer;
 
     public AsyncWebsocketMessageResultEnumerator(WebSocket webSocket, CancellationToken cancellationToken)
     {
@@ -26,9 +26,12 @@ public AsyncWebsocketMessageResultEnumerator(WebSocket webSocket, CancellationTo
 
     public ValueTask DisposeAsync()
     {
-        ArrayPool<byte>.Shared.Return(_receiveBuffer);
+        if (Interlocked.Exchange(ref _receiveBuffer, null) is byte[] toReturn)
+        {
+            ArrayPool<byte>.Shared.Return(toReturn);
+        }
         _webSocket?.Dispose();
-        return new ValueTask(Task.CompletedTask);
+        return default;
     }
 
     public async ValueTask<bool> MoveNextAsync()