Disencumbering a direct charge to zero should delete the debit

[Tiffany Little]

Seen in 3.10 production.

When a direct charge on a PO is spent down to zero or fully disencumbered to $0, the fund debit shows the origin amount as the original amount (lets say $3000) and the amount as 0. But the debit itself remains in the fund. This becomes problematic when a library rolls forward encumbrances and/or money, because the debit still exists so it gets moved into the next year's fund.

We have a library who has been rolling forward encumbrances each year, and they now have a $0 fund debit from 2018.

So the bug request is that when a direct charge is disencumbered fully that the fund debit should be deleted. It would still appear in auditor history so it's not lost forever, but it wouldn't keep getting rolled forward unnecessarily.