Avoid rendenring an empty list in top links

We've had an accessibility error reported by the Spanish "Portal
Administración electrónica" (PAe). While I can't find any accessibility
rule saying empty lists should be avoided, it looks like some screen
readers report finding lists with 0 items, which is annoying.

app/components/layout/top_links_component.html.erb

@@ -1,3 +1,3 @@
 <ul class="no-bullet external-links">
-  <%= raw content_block("top_links", I18n.locale) %>
+  <%= raw top_links_content_block %>
 </ul>

app/components/layout/top_links_component.rb

@@ -1,3 +1,13 @@
 class Layout::TopLinksComponent < ApplicationComponent
   delegate :content_block, to: :helpers
+
+  def render?
+    top_links_content_block.present?
+  end
+
+  private
+
+    def top_links_content_block
+      content_block("top_links", I18n.locale)
+    end
 end

spec/components/layout/top_links_component_spec.rb

@@ -0,0 +1,19 @@
+require "rails_helper"
+
+describe Layout::TopLinksComponent, type: :component do
+  describe "#render?" do
+    it "renders when a content block is defined" do
+      create(:site_customization_content_block, name: "top_links")
+
+      render_inline Layout::TopLinksComponent.new
+
+      expect(page).to have_css "ul"
+    end
+
+    it "does not render when no content block is defined" do
+      render_inline Layout::TopLinksComponent.new
+
+      expect(page).not_to have_css "ul"
+    end
+  end
+end