Fix for #480 and add one test case for that.

[hicqu]

r? @fiveop, thank you.

[hicqu]

why all checks have failed? It a big hit to me because it's the first time I make a pull request on github.
Please help me, thanks. :)

[fiveop]

We don't need the pointer utilities. If you look at #445, you see that we solved the problem in the public interface by changing the parameter type of signal to T: Into<Optional<Signal>>, so that callers can specify None, if they don't want to provide a signal (or in this case no event).

I suggest (again), that you look at the changes made in #445 and base your PR on that.

Thank you for the PR.

[hicqu]

Ok, I got that. I will use Option<&mut SockAddr> instead of pointer magic. New pull request will be later.