Bug 32630: Update get_notice

Make it consider the possibility of a patron not existing.
This ensures that placing a request with partners does not error and works as expected even if the ILL request's borrowernumber is undef

To test:
1) Run the test file before and after applying this patch:
prove t/db_dependent/Koha/ILL/Requests.t

To test (ILL request is kept after borrower is deleted):
1) Apply all patches except this one
2) Enable ILLModule and create an ILL request.
3) Add a type, valid cardnumber and library.
4) Delete the associated borrower.
5) Confirm the ILL request is still listed and shown as expected

Continue test, confirm follow-up bug is fixed:
6) Click 'Place request with partners'
7) You get a ERR_TOO_MANY_REDIRECTS error
8) Apply this patch and restart plack. Repeat.
9) Confirm the place request with partners libraries page is shown correctly

Sponsored-by: UKHSA - UK Health Security Agency
Signed-off-by: Jeremy Evans <Jeremy.Evans@ukhsa.gov.uk>
Signed-off-by: Lisette Scheer <lisette@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>

Koha/ILL/Request.pm

@@ -1905,7 +1905,7 @@ sub get_notice {
         letter_code            => $params->{notice_code},
         branchcode             => $self->branchcode,
         message_transport_type => $params->{transport},
-        lang                   => $self->patron->lang,
+        lang                   => $self->patron ? $self->patron->lang : undef,
         tables                 => {
             illrequests => $self->illrequest_id,
             borrowers   => $self->borrowernumber,