Edited Unassigned: Incorrect check for timeout values [1620]

In ShellStream.cs we see this four times:

> if (timeout != null)
> {...}

Well, _timeout_ is a value type and it will never be "null", meaning in the above expression it wall always evaluate to true.

I fixed it locally by replacing the above with:

> if (timeout.Ticks > 0)
> {...}