Bug 30354: Don't assign warn as letter

TO test:
1 - Check out an item marked for autop renewal to a patron and make it overdue
2 - Set system preference AutoRenewalNotices to follow messaging prefs
3 - set that borrower to receive both email and SMS AUTO_RENEWALS_DGST
4 - confirm your AUTO_RENEWALS_DGST does not have SMS content but does have email
5 - run the auto_renew cron
6 - item is renewed, but error from cron, and cron dies:

No circulation AUTO_RENEWALS_DGST letter transported by sms at /kohadevbox/koha/C4/Letters.pm line 583.
no letter of type 'AUTO_RENEWALS_DGST' found for borrowernumber 5. Please see sample_notices.sql at misc/cronjobs/automatic_renewals.pl line 305.
Can't use string ("1") as a HASH ref while "strict refs" in use at /kohadevbox/koha/C4/Letters.pm line 898.

7 - Apply patch
8 - Make item eligible for auto renewal agian (or checkin/checkout)
9 - Run the cron
10 - There is still 2 warn, but cron does not die:

No circulation AUTO_RENEWALS_DGST letter transported by sms at /kohadevbox/koha/C4/Letters.pm line 583.
no letter of type 'AUTO_RENEWALS_DGST' found for borrowernumber 5. Please see sample_notices.sql at misc/cronjobs/    automatic_renewals.pl line 305.

11 - Patron receives email and item is renewed

Signed-off-by: David Nind <david@davidnind.com>

Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>

misc/cronjobs/automatic_renewals.pl

@@ -328,16 +328,23 @@ sub send_digests {
                     borrowers => $patron->borrowernumber,
                 },
                 message_transport_type => $transport,
-            ) || warn "no letter of type '$params->{letter_code}' found for borrowernumber $borrowernumber. Please see sample_notices.sql";
+            );
 
-            next unless $letter;
+            if ($letter) {
+                C4::Letters::EnqueueLetter(
+                    {
+                        letter                 => $letter,
+                        borrowernumber         => $borrowernumber,
+                        from_address           => $from_address,
+                        message_transport_type => $transport
+                    }
+                );
+            }
+            else {
+                warn
+"no letter of type '$params->{letter_code}' found for borrowernumber $borrowernumber. Please see sample_notices.sql";
+            }
 
-            C4::Letters::EnqueueLetter({
-                letter                 => $letter,
-                borrowernumber         => $borrowernumber,
-                from_address           => $from_address,
-                message_transport_type => $transport
-            });
         }
     }
 }