When the underlying IO returns 0 on read, we must stop polling it since it's closed. Otherwise we'll be stuck in a tight loop. this fixes https://github.com/sfackler/rust-openssl/issues/949
When the underlying IO returns 0 on read, we must stop polling it since it's closed. Otherwise we'll be stuck in a tight loop. this fixes https://github.com/sfackler/rust-openssl/issues/949