WebUI: Fix incorrect subcategory sorting

PR #19833.
Closes #19756.

src/webui/www/private/scripts/client.js

@@ -488,7 +488,21 @@ window.addEvent('load', function() {
         Object.each(category_list, function(category) {
             sortedCategories.push(category.name);
         });
-        sortedCategories.sort();
+        sortedCategories.sort(function(category1, category2) {
+            for (let i = 0; i < Math.min(category1.length, category2.length); ++i) {
+                if (category1[i] === "/" && category2[i] !== "/") {
+                    return -1;
+                }
+                else if (category1[i] !== "/" && category2[i] === "/") {
+                    return 1;
+                }
+                else if (category1[i] !== category2[i]) {
+                    return category1[i].localeCompare(category2[i]);
+                }
+            }
+
+            return category1.length - category2.length;
+        });
 
         for (let i = 0; i < sortedCategories.length; ++i) {
             const categoryName = sortedCategories[i];