asyncwrap: fix constructor condition for early ret

AsyncWrap should always properly propagate asynchronous calls to any
child that is created. Regardless whether kCallInitHook is currently
active. The previous logic would always return early if kCallInitHook
wasn't set.

PR-URL: https://github.com/iojs/io.js/pull/732


Reviewed-by: Ben Noordhuis <info@bnoordhuis.nl>