fix https://github.com/DarthAffe/OBD.NET/issues/3

OBD.NET/OBD.NET.Common/Devices/SerialDevice.cs

@@ -222,6 +222,8 @@ namespace OBD.NET.Devices
             while (!commandCancellationToken.IsCancellationRequested)
             {
                 currentCommand = null;
+                try
+                {
                     if (commandQueue.TryTake(out currentCommand, Timeout.Infinite, commandCancellationToken.Token))
                     {
                         Logger?.WriteLine("Writing Command: '" + currentCommand.CommandText.Replace('\r', '\'') + "'", OBDLogLevel.Verbose);
@@ -239,6 +241,9 @@ namespace OBD.NET.Devices
                         commandFinishedEvent.WaitOne();
                     }
                 }
+                catch (OperationCanceledException)
+                {/*ignore, because it is thrown when the cancellation token is canceled*/}
+            }
         }
 
         /// <summary>
@@ -246,6 +251,7 @@ namespace OBD.NET.Devices
         /// </summary>
         public virtual void Dispose()
         {
+            commandQueue.CompleteAdding();
             commandCancellationToken?.Cancel();
             commandWorkerTask?.Wait();
             Connection?.Dispose();