The billed quantity field on the purchase order line
must exclude the cancelled invoice, as a cancelled invoice
is not considered as invoiced.

`draft` could be considered as well, but we do not
take the chance now, as this field is used
when creating a new invoice, to determine the
quantity to invoice. Therefore, if there are
draft invoices with some quantities invoiced,
it can make sense to reduce the quantity
in this new invoice. Nevertheless, it must not be the case
for cancelled invoices.

opw-679363