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