Bug 14390: [Follow-up] Only update FU record in UpdateFine

Bug 14390: [Follow-up] Only update FU record in UpdateFine

Exclude O, F and M when outstanding == 0.
Check if the issue_id points to a FU record.

Note: We only warn now when we see a second FU record with this issue id.
That should be a rare exception. As before, we are just counting it in
our total. Added a FIXME.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Tested fine on overdue. Renewed and backdated for a second fine. The F
and FU can be seen on the Fines tab and are totaled on Check out.

Signed-off-by: Jacek Ablewicz <abl@biblos.pk.edu.pl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>