test: increase coverage for punycode's decode

Added test cases for error.

PR-URL: https://github.com/nodejs/node/pull/10940


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>