Bug 34532: Silence warns in Patroncard.pm

Bug 34532: Silence warns in Patroncard.pm

To test:

1. Go to patron card creator and make a patron card batch, card layout, and card template.
2. In the card layout leave some values blank for Lower left X coordinate and Lower left Y coordinate.
3. Now go create a card batch while tailing the plack-intranet-error log/
4. Notice in the logs:

[2023/08/14 20:50:54] [WARN] Argument "" isn't numeric in multiplication (*) at /kohadevbox/koha/C4/Patroncards/Patroncard.pm line 109.
[2023/08/14 20:50:54] [WARN] Argument "" isn't numeric in multiplication (*) at /kohadevbox/koha/C4/Patroncards/Patroncard.pm line 248.
[2023/08/14 20:50:54] [WARN] Argument "" isn't numeric in multiplication (*) at /kohadevbox/koha/C4/Patroncards/Patroncard.pm line 249.

5. Apply patch, restart_all
6. Try again and notice the WARNS should be gone from the logs now.
7. Make sure you can still create patron cards and the PDF's the generate look right.

Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>