FIX: quoted private topic url respects subfolder install (#25643)

Fixes an issue where private topics that are quoted have an incorrectly formatted url when using a subfolder install.

This update returns a relative url that includes the base_path rather than a combination of base_url + base_path.

spec/models/topic_spec.rb

@@ -311,6 +311,24 @@ RSpec.describe Topic do
     end
   end
 
+  describe "slugless_url" do
+    fab!(:topic)
+
+    it "returns the correct url" do
+      expect(topic.slugless_url).to eq("/t/#{topic.id}")
+    end
+
+    it "works with post id" do
+      expect(topic.slugless_url(123)).to eq("/t/#{topic.id}/123")
+    end
+
+    it "works with subfolder install" do
+      set_subfolder "/forum"
+
+      expect(topic.slugless_url).to eq("/forum/t/#{topic.id}")
+    end
+  end
+
   describe "updating a title to be shorter" do
     let!(:topic) { Fabricate(:topic) }