user upgrades: make upgrade page visible to logged out users.

app/controllers/user_upgrades_controller.rb

@@ -1,5 +1,5 @@
 class UserUpgradesController < ApplicationController
-  before_action :member_only, :only => [:new, :show]
+  before_action :member_only, only: [:show]
   helper_method :user
   skip_before_action :verify_authenticity_token, only: [:create]
 

app/views/user_upgrades/new.html.erb

@@ -106,7 +106,9 @@
     </div>
 
     <% if Danbooru.config.stripe_publishable_key %>
-      <% if CurrentUser.safe_mode? %>
+      <% if CurrentUser.is_anonymous? %>
+        <p><%= link_to "Sign up", new_user_path %> or <%= link_to "login", new_session_path(url: new_user_upgrade_path) %> first to upgrade your account.</p>
+      <% elsif CurrentUser.safe_mode? %>
         <%= render "stripe_payment" %>
       <% else %>
         <%= render "stripe_payment_safebooru" %>