[FIX] product: Fixed product's main supplier for multi-company scenario....

...(maintenance: 618809)

Currently in multi-company environment, there is possibility that the procurement may generate the PO with the supplier of other company(which is not accessible by the users of current company and even if the product has a supplier from the current company).

Detailed steps are available at #3833 

This branch fixes this issue, kindly review it.

Thanks.