* FIX not possible to search for billed and not billed supplier orders in the list
as the current implemenation the $billed var can be either 0 or 1 but cannot be empty if both should be searched. This prevents searching an supplier order through the general search functionality as it finds only not yet billed orders.
* Update list.php
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Co-authored-by: Laurent Destailleur <eldy@destailleur.fr>
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