Address issue #1818 where MqttConnectionContext throws an error when passed a...

Address issue #1818 where MqttConnectionContext throws an error when passed a TcpConnection. (#1819)

* Address issue #1818 where MqttConnectionContext throws and error when passed a TcpConnection.

* Update ReleaseNotes.md

---------
Co-authored-by: NChristian <6939810+chkr1011@users.noreply.github.com>

.github/workflows/ReleaseNotes.md

@@ -3,3 +3,4 @@
 * [Server] Fixed _NullReferenceException_ in retained messages management (#1762, thanks to @logicaloud).
 * [Server] Exposed new option which allows disabling packet fragmentation (#1753).
 * [Server] Expired sessions will no longer be used when a client connects (#1756).
+* [Server] Fixed an issue in connection handling for ASP.NET connections (#1819, thanks to @CZEMacLeod).

Source/MQTTnet.AspnetCore/MqttConnectionContext.cs

@@ -33,8 +33,11 @@ namespace MQTTnet.AspNetCore
             PacketFormatterAdapter = packetFormatterAdapter ?? throw new ArgumentNullException(nameof(packetFormatterAdapter));
             _connection = connection ?? throw new ArgumentNullException(nameof(connection));
 
-            _input = connection.Transport.Input;
-            _output = connection.Transport.Output;
+            if (!(_connection is TcpConnection tcp) || tcp.IsConnected)
+            {
+                _input = connection.Transport.Input;
+                _output = connection.Transport.Output;
+            }
         }
 
         public long BytesReceived { get; private set; }