Created invoice with only direct charges not linked to PO

[Tiffany Little]

Tested on 3.4.

To test:
1. Have an on-order purchase order.
2. From within the purchase order, click the Create Invoice button.
3. Give the invoice some bare details, Invoice ID, receiver, and at least one *new* direct charge. There should be no line items or direct charges from the PO.
4. Save the invoice and return to the PO.
5. The invoice is not included in the Invoices () count on the purchase order.

Because I created the invoice from *within* the purchase order, from a UX standpoint I'd expect that the invoice would inherit the PO ID when I create a direct charge and it would be linked to that PO.

My real-life example for this might be that a vendor sends an invoice with only a direct charge on it, like for cataloging / processing. We didn't include a direct charge on the PO for that, because due to another bug / preference, that would be double booking the direct charge. I would go to the PO, create an invoice with this new direct charge, and expect that I should see Invoices (1) on my purchase order because this is related to this PO. But you don't. The invoice is searchable by Vendor Invoice ID, but it's not related to the PO in any way.

[Christine Morgan (cmorgan-z)]

Tested in 3.5.1.