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: Mason James <mtj@kohaaloha.com>