Bug 15711: Fixing the 'Delete selected' button on patroncard images

Bug 15711: Fixing the 'Delete selected' button on patroncard images

To test:
1) Go to Tools -> Patron Card Creator -> Manage images
2) Upload an image if you haven't already
3) Click Delete selected without selecting any images
4) Notice broken behaviour as described in Description
5) Apply patch, refresh page
6) Click Delete selected without selecting any images
7) Notice alert. Click OK
8) Select one image or more, click Delete selected
9) Notice confirm delete message.

Sponsored-by: Catalyst IT
Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit bd3879e037727cdc2cc851aa910c68bd257ee6f4)
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
(cherry picked from commit 70c55a6d69d68e04b50e8fbcf0eb7e62457350d7)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>