Pr/check destination null

[tmatthey]

Remove Debug.Assert(ok);, just return value of m_commandPipe.TryRead. I'm not certain if caller of Mailbox.TryRead may check if command.Destination to be not zero when processing the command, i.e., reading a command with CommandType.Done sent by ZObject.SendDone(), which has no destination.

[tmatthey]

Is there a any chance that any can review and merge my PR? And is there a plan to release a new patch version including this PR? For now we running our application with a debug version including the changes of this PR and we have not seen any exceptions so far. Thanks in advance.

[drewnoakes]

I'm interested to know why you had to defend against a null command in those places.

Also bumping xUnit has created some new warnings. Could you fix those up please, so we have a clean build? Thanks.

[tmatthey]

@drewnoakes, you are right, it was not where I got the actual exception. I fixed all the warnings and put all the task awaiting into a separate class and resolves all your findings.

Process terminated. Assertion failed.
   at NetMQ.Core.Mailbox.TryRecv(Int32 timeout, Command& command)
   at NetMQ.Core.SocketBase.ProcessCommands(Int32 timeout, Boolean throttle, CancellationToken cancellationToken)
   at NetMQ.Core.SocketBase.GetSocketOptionX(ZmqSocketOption option)
   at NetMQ.NetMQSocket.GetSocketOptionX[T](ZmqSocketOption option)
   at NetMQ.NetMQSocket.get_HasIn()

[tmatthey]

@drewnoakes did got any chance to take a look? With the last revert it is just removal of assert and oppgrade of System.ServiceModel.Primitives 4.10.3. Is there any chance to get en new patch release includeing this PR? Thanks in advance.