Validation should be done on PO when updating from notification

If allowing Edit from Notification link, there should be validation done on save before Approval is attempted.

Just like when creating new PO line or editing existing PO line.

Test case:

Create Standard Purchase Order nnnn with 1 line with 100001 quantity

create shipment and quantity equal to line.

Click Approve - set to go to next Approver.

Log in as next approver, and move to approval notification - click on Edit PO link

Split the Distribution into 2 - enter 999,988.00 on 1 dist and 2.00 on the other - so less quantity then line

Save and Submit for approval - no error message is given at this point - so looks like no validation is done