HFP-3918 Fix crash when going to non-existent slide

src/scripts/cp.js

@@ -908,6 +908,10 @@ CoursePresentation.prototype.attachElements = function ($slide, index) {
     return; // Already attached
   }
 
+  if (index < 0 || index > this.slides.length - 1) {
+    return; // Slide does not exist
+  }
+
   var slide = this.slides[index];
   var instances = this.elementInstances[index];
   if (slide.elements !== undefined) {
@@ -1848,6 +1852,10 @@ CoursePresentation.prototype.attachAllElements = function () {
  * @returns {Boolean} Always true.
  */
 CoursePresentation.prototype.processJumpToSlide = function (slideNumber, noScroll, handleFocus) {
+  if (slideNumber < 0 || slideNumber > this.slides.length - 1) {
+    return;
+  }
+
   var that = this;
   if (this.editor === undefined && this.contentId) { // Content ID avoids crash when previewing in editor before saving
     var progressedEvent = this.createXAPIEventTemplate('progressed');
@@ -2039,7 +2047,11 @@ CoursePresentation.prototype.setOverflowTabIndex = function () {
 CoursePresentation.prototype.setSlideNumberAnnouncer = function (slideNumber, handleFocus = false) {
   let slideTitle = '';
 
-  if (!this.navigationLine) {
+  if (
+    !this.navigationLine ||
+    slideNumber < 0 ||
+    slideNumber >= this.slides.length - 1
+  ) {
     return slideTitle;
   }
 

src/scripts/navigation-line.js

@@ -419,6 +419,10 @@ const NavigationLine = (function ($) {
   NavigationLine.prototype.updateProgressBar = function (slideNumber, prevSlideNumber, solutionMode) {
     var that = this;
 
+    if (slideNumber < 0 || slideNumber > this.cp.progressbarParts.length - 1) {
+      return; // Slide number is out of bounds
+    }
+
     // Updates progress bar progress (blue line)
     var i;
     for (i = 0; i < that.cp.progressbarParts.length; i += 1) {
@@ -489,7 +493,7 @@ const NavigationLine = (function ($) {
     const $part = this.cp.progressbarParts[index];
     const $partTitle = $part.find('.h5p-progressbar-part-title');
     const answeredLabel = this.answeredLabels[state].replace('@slideName', this.createSlideTitle(index));
-    
+
     $partTitle.html(`${answeredLabel}`);
   };