fixing mailer previews for apps with globbing route

actionmailer/lib/action_mailer/railtie.rb

@@ -41,7 +41,7 @@ module ActionMailer
         options.each { |k,v| send("#{k}=", v) }
 
         if options.show_previews
-          app.routes.append do
+          app.routes.prepend do
             get '/rails/mailers'         => "rails/mailers#index"
             get '/rails/mailers/*path'   => "rails/mailers#preview"
           end

railties/test/application/mailer_previews_test.rb

@@ -40,6 +40,17 @@ module ApplicationTests
       assert_equal 404, last_response.status
     end
 
+    test "/rails/mailers is accessible with globbing route present" do
+      app_file "config/routes.rb", <<-RUBY
+        Rails.application.routes.draw do
+          get '*foo', to: 'foo#index'
+        end
+      RUBY
+      app("development")
+      get "/rails/mailers"
+      assert_equal 200, last_response.status
+    end
+
     test "mailer previews are loaded from the default preview_path" do
       mailer 'notifier', <<-RUBY
         class Notifier < ActionMailer::Base