Discard invoice line

The issue is that the user normally discard the line at invoice level and then cancell the invoice.

But in this scenario user by mistakenly cacelled the invoice without discarding the line at invoce level. and he entered the amount wrong.

Now the po #34198499 has been utilized fully and created new invoice for the po #34198499. But the invoice #5968CANCELA has fully utilized the amount which is fund allocated.