Code review comment for lp:~ralfjung-e/mailman/2.1

If line 20 (in the patch below) sets "captcha_idx = 0" python throws an error:

   TypeError: cannot concatenate 'str' and 'int' objects

I think a better solution would be to remove the captcha_idx from that section of code if it is None, (and set it to None at line 20).