crypto: add more keylen sanity checks in pbkdf2

issue #2987 makes the point that crypto.pbkdf2 should not fail silently
and accept invalid but numeric values like NaN and Infinity. We already
check if the keylen is lower than 0, so extending that to NaN and
Infinity should make sense.

Fixes: https://github.com/nodejs/node/issues/2987

PR-URL: https://github.com/nodejs/node/pull/3029


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>