tls: emit errors on close whilst async action

When loading session, OCSP response, SNI, always check that the
`self._handle` is present. If it is not - the socket was closed - and we
should emit the error instead of throwing an uncaught exception.

Fix: https://github.com/joyent/node/issues/8780
Fix: https://github.com/iojs/io.js/issues/1696
PR-URL: https://github.com/nodejs/io.js/pull/1702


Reviewed-By: Trevor Norris <trev.norris@gmail.com>