There was an unnecessary quadratic loop in idna decoding. This restores
the behavior to linear.
(cherry picked from commit d315722564)
(cherry picked from commit a6f6c3a3d6)
Co-authored-by: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>