Bug 6796: Don't add a day if hourly loan period pushes due date

Bug 6796: Don't add a day if hourly loan period pushes due date

If ConsiderLibraryHoursWhenIssuing is set to shorten the loan period to
the closing time, if the loan period initially pushes the due date to
the following day, the day still gets added when calculating the due
date. We simply need to hardcode the due time here as the due day is the
same as the issue day.

We only need to calculate a due date if ConsiderLibraryHoursWhenIssuing
is set to extend the loan period to the next opening day, as we'll need
to consider holidays/closed days.

Sponsored-by: Catalyst IT
Sponsored-by: Auckland University of Technology
Signed-off-by: Sam Lau <samalau@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>