def keylist_next
      rkey = []
      err = GPGME::gpgme_op_keylist_next(self, rkey)
      exc = GPGME::error_to_exception(err)
      raise exc if exc
      rkey[0]
    end
def keylist_next
      rkey = []
      err = GPGME::gpgme_op_keylist_next(self, rkey)
      exc = GPGME::error_to_exception(err)
      raise exc if exc
      rkey[0]
    end
Advance to the next key in the key listing operation.

 Used by {GPGME::Ctx#each_key}