Fix 500 when initializing an occurrence on a draft recurring meeting template

InitOccurrenceService#draft_template_failure returned only a message
with no errors:, which crashed the API layer's
ErrorBase.create_and_merge_errors(call.errors) with an ArgumentError
("expected at least one error") when it tried to build a MultipleErrors
response from an empty error list. Every recurring meeting's template is
in draft state right after creation, so initializing its first occurrence
before moving the template out of draft always hit this 500 instead of a
clean 422.

Populate the recurring meeting's own errors object before returning
failure, matching the errors: shape used elsewhere in this service and
across the codebase.

Author: jtauschl

modules/meeting/app/services/recurring_meetings/init_occurrence_service.rb

@@ -62,7 +62,8 @@ def perform
     end
 
     def draft_template_failure
-      ServiceResult.failure(message: I18n.t("recurring_meeting.occurrence.error_template_draft"))
+      recurring_meeting.errors.add(:base, I18n.t("recurring_meeting.occurrence.error_template_draft"))
+      ServiceResult.failure(errors: recurring_meeting.errors)
     end
 
     def validate_contract

modules/meeting/spec/services/recurring_meetings/init_occurrence_service_spec.rb

@@ -67,6 +67,15 @@
         expect(created_meeting).to be_nil
       end
 
+      it "carries a non-empty errors object usable by the API layer" do
+        # Regression test: draft_template_failure used to return only a
+        # message with no errors:, which crashed
+        # API::Errors::ErrorBase.create_and_merge_errors(call.errors) with an
+        # ArgumentError ("expected at least one error") when the API route
+        # tried to build a MultipleErrors response from an empty error list.
+        expect(service_result.errors).not_to be_empty
+      end
+
       it "does not add an occurrence" do
         expect { instance.call(**params) }
           .not_to change { series.meetings.not_templated.count }