[FIX] stock: creation of stock inventory adjustement

The system cannot create two inventory adjustements in state 'in Progess'
with the same product, with the same location, same package, same lot and
same owner.
Example:if two adjustments(ADJ1, ADJ2) are created with the same product(P)
and with the same location(L), let's say:
qty_available for P is 10
in ADJ1: Theoritical Quantity=10 and Real Quantity=20 => a quant with +10 is created
in ADJ2: Theoritical Quantity=10 and Real Quantity=30 => a quant with +20 is created

When ADJ1 is validated then qty_available for P is now 20(that 's ok)
When ADJ2 is validated then qty_available for P is now 40(that's wrong because
the Real Quantity is expected which is 30)

This is why this fix is required.

opw:660658