Bug 16151: Restore the ability to place holds from lists at the OPAC

 Bug 16151: Restore the ability to place holds from lists at the OPAC

This patch fixes a bug introduced by bug 14544.
Holds can not be placed from lists at the OPAC, the action results in a
crash:
Can't call method "field" on an undefined value at
/home/koha/src/C4/Items.pm line 1504.
 at /home/koha/src/opac/opac-reserve.pl line 601

Before 14544, the checkboxes were named 'ACT-$BIBNUM', something like
REM-4242. Now we can retrieve the biblionumber from the value.

Test plan:
Select a public list
check some titles and click on the 'Place hold' link
you should able to process the reservation

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>