Allow redirects to external paths when creating a user account

Author: Redande

Diff for: app/controllers/users_controller.rb

@@ -15,7 +15,7 @@ def index
   def new
     authorize! :create, User
     alternative_location = SiteSetting.all_settings['signup_location']
-    return redirect_to alternative_location if alternative_location
+    return redirect_to(alternative_location, allow_other_host: true) if alternative_location
     add_breadcrumb 'Sign up', new_user_path
 
     if signed_in?