Fixed possible coroutine leaks caused by closing the connection with SetDeadline

[blinkbean]

Resolves #250
See detailed description in the fore-mentioned issue.

[xtaci]

need description on this issue

[faddat]

@xtaci I think that the issue is that we'd always return nil previously.

I'm trying to learn the codebase, and what I think that these changes do is explicitly send back a connection close.

I think that the author could be correct.