fs: throw on invalid callbacks for async functions

If an asynchronous function is passed no callback function, there is no
way to return the result. This patch throws an error if the callback
passed is not valid or none passed at all.

PR-URL: https://github.com/nodejs/node/pull/12562



Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>