FIX: error when flagging to notify moderators because message title is too long

app/models/post_action.rb

@@ -245,7 +245,7 @@ SQL
     title = I18n.t("post_action_types.#{post_action_type}.email_title", title: post.topic.title, locale: SiteSetting.default_locale)
     body = I18n.t("post_action_types.#{post_action_type}.email_body", message: opts[:message], link: "#{Discourse.base_url}#{post.url}", locale: SiteSetting.default_locale)
     warning = opts[:is_warning] if opts[:is_warning].present?
-    title = title.truncate(255, separator: /\s/)
+    title = title.truncate(SiteSetting.max_topic_title_length, separator: /\s/)
 
     opts = {
       archetype: Archetype.private_message,

spec/models/post_action_spec.rb

@@ -619,6 +619,13 @@ describe PostAction do
       end
     end
 
+    it "should succeed even with low max title length" do
+      SiteSetting.max_topic_title_length = 50
+      post.topic.title = 'This is a test topic ' * 2
+      post.topic.save!
+      message_id = PostAction.create_message_for_post_action(Discourse.system_user, post, PostActionType.types[:notify_moderators], message: "WAT")
+      expect(message_id).to be_present
+    end
   end
 
   describe ".lookup_for" do