Bug fix for 'List all users'

The changes made here: https://github.com/thorsten/phpMyFAQ/commit/8ca2644742bf9e71a041c62ffb92611905c9cb15 have caused a bug in the admin page 'List all users'.

It turns out blocked users aren't being loaded, which stops us from activating new members. The last valid user is repeated for each blocked user.

> ![Image of bug in action](http://arduino.land/Images/FAQ/Debug/duplicate-users.png)

I think the change is needed to prevent blocked users from doing things?
My change modifies the function getUserById to allow blocked users if needed, but are denied by default.