Properly creating Jeeqser_Challenge if it was requested, but did not exist. (#155)

Hi Ali,

Seems the code was ported to NDB already; the issue was that the method expected NDB key as an object but was getting it as a urlsafe string.

However, a comment said that this part of code should've never been triggered - Jeeqser_Challenge should've been created elsewhere.
Should I investigate this, or that's just a leftover of DB migration?


Fixes #155.