[FIX] website_slides: do not crash if there is any issue loading quiz data

Template displaying quiz should not crash if call to server did not answer
correctly. Minimal fix is to have void data to display. Real issue is that
unreadable quiz should not be displayed. This will be fixed in an upcoming
fix.

Task 2058595 (eLearning v13 testing)
Task 2064863 (quiz bug report)

addons/website_slides/static/src/js/slides_course_quiz.js

@@ -92,8 +92,9 @@ odoo.define('website_slides.quiz', function (require) {
             }
             else if (alert_code === 'slide_quiz_done') {
                 message = _t('This quiz is already done. Retaking it is not possible.');
-            } else if (alert_code === 'public_user') {
-                message = _t("You must be logged to submit the quiz.");
+            }
+            else if (alert_code === 'public_user') {
+                message = _t('You must be logged to submit the quiz.');
             }
             this.$('.o_wslides_js_lesson_quiz_error span:first').html(message);
             this.$('.o_wslides_js_lesson_quiz_error').removeClass('d-none');
@@ -112,10 +113,10 @@ odoo.define('website_slides.quiz', function (require) {
                 }
             }).then(function (quiz_data) {
                 self.quiz = {
-                    questions: quiz_data.slide_questions,
-                    quizAttemptsCount: quiz_data.quiz_attempts_count,
-                    quizKarmaGain: quiz_data.quiz_karma_gain,
-                    quizKarmaWon: quiz_data.quiz_karma_won
+                    questions: quiz_data.slide_questions || [],
+                    quizAttemptsCount: quiz_data.quiz_attempts_count || 0,
+                    quizKarmaGain: quiz_data.quiz_karma_gain || 0,
+                    quizKarmaWon: quiz_data.quiz_karma_won || 0,
                 };
             });
         },