Bug 21611: Fix priority dropdown for holds

Bug 21611: Fix priority dropdown for holds

To Test:
 1 - Find a record
 2 - Place several holds some with differing pickup locations
 3 - Check in one hold to confirm as waiting
 4 - Check another in to set a hold in transit
 5 - View the holds queue for the record:
    /cgi-bin/koha/reserve/request.pl?biblionumber=##
 6 - Confirm found holds are incorrect
 7 - Apply patch
 8 - Reload
 9 - Confirm holds look correct
10 - Alter the values of HoldsSplitQueue and HoldsSplitQueueNumbering
11 - Confirm things still look right

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>