move extended description presenter to own method

app/presenters/instance_presenter.rb

@@ -65,4 +65,8 @@ class InstancePresenter
   def mascot
     @mascot ||= Rails.cache.fetch('site_uploads/mascot') { SiteUpload.find_by(var: 'mascot') }
   end
+
+  def extended_description
+    site_extended_description.html_safe.presence
+  end
 end

app/views/about/more.html.haml

@@ -43,4 +43,4 @@
 
   .column-3
     .box-widget
-      .rich-formatting= @instance_presenter.site_extended_description.html_safe.presence || t('about.extended_description_html')
+      .rich-formatting= @instance_presenter.extended_description || t('about.extended_description_html')