Bug 16387: Fix default shortened loan period time

Bug 16387: Fix default shortened loan period time

When a loan period is shortened due to using decreaseLoanHighHolds* the time is
always set to the current time in X days, even if the original loan period is
given in days and not in hours.

It should default to 23:59 as is normal for loan periods given in days.

As original due date time defaults to 23:59 when given in days, this patch
modifies the hours and minutes of shortened due date to be equal to original due
date.

To test:
1. prove t/db_dependent/DecreaseLoanHighHolds.t

Signed-off-by: Grace McKenzie <grace.mcky@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 21ac9fcdc2ca449a491cc79e68cc854ee248d911)
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>