Bug 35263: Default 'can_place_ill_in_opac' to 1

Bug 35263: Default 'can_place_ill_in_opac' to 1

If ILLModule sys pref is 'off', this input param is undef. The database does not allow it to be nullable causing an error.
Check if its defined (i.e. the option was submitted) and use that, if not default to 1

Test plan, k-t-d:
1) Edit an existing patron category, visit:
/cgi-bin/koha/admin/categories.pl?op=add_form&categorycode=B
2) Click 'Save' at the bottom of the form
3) Notice a yellow box is shown with an error message
4) Apply patch. Repeat steps 1-3. Notice it now updates successfully.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>