[FIX] purchase: move with zero qty

- Create a product FIFO / Real-Time valuation
- Create a PO with 1 unit, validate, receive the picking
- Create the corresponding vendor bill, but do not validate
- Unlock the picking and change the received quantity to 0.0
- Validate the invoice

A traceback because of a zero division occurs.

When searching for the stock moves linked to the PO, we should filter
out the ones with a zero quantity.

opw-1843543