FIX: Error in CSS generation for anon on login_required (#20978)

Followup to 6ad9e4ad06,
I was not aware that `site.categories` is undefined if
the user is anon and the site is login_required, this
handles that scenario and does not continue trying to
generate CSS.

app/assets/javascripts/discourse/app/initializers/category-color-css-generator.js

@@ -12,6 +12,11 @@ export default {
   initialize(container) {
     this.site = container.lookup("service:site");
 
+    // If the site is login_required and the user is anon there will be no categories preloaded.
+    if (!this.site.categories) {
+      return;
+    }
+
     const generatedCssVariables = [
       ":root {",
       ...this.site.categories.map(

app/assets/javascripts/discourse/app/initializers/hashtag-css-generator.js

@@ -14,6 +14,15 @@ export default {
    * ones in core are CategoryHashtagType and TagHashtagType.
    */
   initialize(container) {
+    this.site = container.lookup("service:site");
+
+    // If the site is login_required and the user is anon there will be no categories
+    // preloaded, so there will be no category color CSS variables generated by
+    // the category-color-css-generator initializer.
+    if (!this.site.categories) {
+      return;
+    }
+
     let generatedCssClasses = [];
 
     Object.values(getHashtagTypeClasses()).forEach((hashtagTypeClass) => {

app/assets/javascripts/discourse/app/lib/hashtag-types/category.js

@@ -9,7 +9,7 @@ export default class CategoryHashtagType extends HashtagTypeBase {
   }
 
   get preloadedData() {
-    return this.site.categories;
+    return this.site.categories || [];
   }
 
   generateColorCssClasses(model) {

app/assets/javascripts/discourse/tests/acceptance/css-generator-test.js

@@ -1,4 +1,4 @@
-import { acceptance } from "discourse/tests/helpers/qunit-helpers";
+import { acceptance, exists } from "discourse/tests/helpers/qunit-helpers";
 import { visit } from "@ember/test-helpers";
 import { test } from "qunit";
 
@@ -30,3 +30,19 @@ acceptance("CSS Generator", function (needs) {
     );
   });
 });
+
+acceptance(
+  "CSS Generator | Anon user in login_required site",
+  function (needs) {
+    needs.site({ categories: null });
+    needs.settings({ login_required: true });
+
+    test("category CSS variables are not generated", async function (assert) {
+      await visit("/");
+      const cssTag = document.querySelector(
+        "style#category-color-css-generator"
+      );
+      assert.notOk(exists(cssTag));
+    });
+  }
+);