Bug 15415: Warn when creating a new print profile

Bug 15415: Warn when creating a new print profile

As per Jonathan's comment in Comment 3, I've put that line of code in an
if statement that will only call the get_attr method if we are editing
an existing profile (therefore the profile id will exist).

To test:
1) Go to Tools -> Patron Card Creator -> New printer profile
2) Notice warn
3) Apply patch
4) Refresh page
5) Confirm warn is gone and page still works as expected

Sponsored-by: Catalyst IT
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 47e80e899aca7c79aaeb58350401a1963fbe709d)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>