When the order line as a supplier/customer product, we should allow to select
blanket agreement line with the same product or without any product. Because
the supplier/customer product may be added after the blanket agreement is
running.
Closes#12909
(grafted from c397ef500313f85fc7f3552786e98237d4036441)
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branch : 7.0
Cédric Krier
681443282e