IT gh#785

#785 Vendor empty returns missing in invoice cand when negativ qty

Testcase to check if all vendor empty returns create correct invoice candidates.

1. Make sure G000X is not a vendor with invoice type Produzentenabrechnung, and has no flatrate contract for Gebinde

2. In Wareneingang POS, create empty returns for G000X (vendor):
   • TU A: 10
   • LU C: 5
3. Check the inout that was created, and the invoice candidates for it:
   • => doc type: Leergutausgabe, status: completed
   • => 2 inout lines, with HUs and qties as set
   • => 2 invoice candidates, with neg. qty, and resp. prices
4. Reactivate the inout, and add an inout line using copy:
   • change the HU to TU B, and set the qty to -3
   • save & complete
5. Check the invoice candidates:
   • => additional IC for TU B, with qty: 3, and resp. price
6. Create the invoice:
   • => doctype: Gutschrift Lieferant
   • => neg. qties and prices for TU A and LU C
   • => pos. qty and price for TU B
   • => overall Total is correctly calculated
   • => no neg. qties in Jasper, the qties from returns are displayed in Retour!
7. In Wareneingang POS, create another empty returns for G000X (vendor):
   • TU B: 15
   • LU C: 2
8. Check the inout that was created, and the invoice candidates for it:
   • => doc type: Leergutausgabe, status: completed
   • => 2 inout lines, with HUs and qties as set
   • => 2 invoice candidates, with neg. qty, and resp. prices
9. Reactivate the inout, and add an inout line using new:
   • change the HU to TU A, and set the qty to -5
   • set the right posting type
   • save & complete
10. Check the invoice candidates:
    • => additional IC for TU A, with qty: 5, and resp. price
11. Create the invoice:
    • => doctype: Gutschrift Lieferant
    • => neg. qties and prices for TU B and LU C
    • => pos. qty and price for TU A
    • => overall Total is correctly calculated
    • => no neg. qties in Jasper, the qties from returns are displayed in Retour!
12. Repeat testing for G000X as customer (Leergutrücknahme), to make sure it works fine there too
    • => doctype: Gutschrift