Fix EZP-21365: eZ Password Expiry support for users with main location outside "Users"

As in topic. We have a users with second (and main) location under 'Content structure'. Without this fix ezmbpaex_updatechildren cronjob doesn't update Password Expiration attributes.

And $add_paex_to_update from line 397 seems to be an array, not an object.

cheers,
Bogdan