Bug 21093: In additem.pl set the right stickyduedate for fast add

Bug 21093: In additem.pl set the right stickyduedate for fast add

To test:
-1 Set the specify due date option to a date, don't check the checkbox
-2 Enter an unknown barcode
-3 Click on fast add
-4 Add a record
-5 Add an item (don't change the barcode!)
-6 The item is checked out to the patron
-7 Verify: The checkbox is "Remember for session" is checked now
-8 APPLY patch
-9 Do steps 1-6 again, this time "Remember for session" should be unchecked
-10 Do steps 1-6 again but this time do check the "Remember for session" checkbox.
-11 It should be properly checked

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>