python: More type conversion fixes.
python: More type conversion fixes.

* lang/python/helpers.c (pyPassphraseCb): Cope with 'uid_hint' being
NULL, convert it to an Unicode object, and cope with the callback
returning both Unicode and bytes objects.

Signed-off-by: Justus Winter <4d1bd7a5ca1cd26bee0df05b6801a6ce9a22196e@gnupg.org>

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme