Bug 10910: Add a warning when deleting a patron with pending suggestions

Bug 10910: Add a warning when deleting a patron with pending suggestions

Test plan:
From the OPAC, add a suggestion
From the staff interface, try to delete the patron who created the
suggestion
=> You get a warning message

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>