[BUGFIX] check for imageUrls where empty nested arrays returned false positives (kitodo#1706)

Co-authored-by: Sebastian Meyer <sebastian.meyer@opencultureconsulting.com>

Author: fschoelzel

Resources/Public/JavaScript/PageView/PageView.js

@@ -832,7 +832,7 @@ dlfViewer.prototype.displayHighlightWord = function(highlightWords = null) {
  */
 dlfViewer.prototype.init = function(controlNames) {
 
-    if (this.imageUrls.length <= 0)
+    if (!dlfUtils.hasContent(this.imageUrls))
         throw new Error('Missing image source objects.');
 
     this.initLayer(this.imageUrls)

Resources/Public/JavaScript/PageView/Utility.js

@@ -532,6 +532,27 @@ dlfUtils.getUrlParam = function (param) {
     return null;
 };
 
+/**
+ * Check if an array (possibly nested) contains at least one non-empty value.
+ *
+ * @param {Array} arr - The array to check (may be nested).
+ * @returns {boolean} True if at least one non-empty value exists, false otherwise.
+ */
+dlfUtils.hasContent = function(arr) {
+    if (!Array.isArray(arr)) {
+        return false;
+    }
+
+    return arr.some(item => {
+        if (Array.isArray(item)) {
+            // Recurse into nested arrays
+            return dlfUtils.hasContent(item);
+        }
+        // Check primitive values: must not be null/undefined/empty-string
+        return item !== null && item !== undefined && String(item).trim() !== "";
+    });
+};
+
 /**
  * Returns true if the specified value is null.
  * @param {?} val