FIX: post edited webhook does not reflect updated topic title

This fix ensures that when a topic title is edited the new title shows
up in the post webhook instead of the old title.

Rather than passing in the old topic object to the PostRevisor the
PostRevisor initializer will load the updated topic object inside of the
initializer if you don't pass it in. This will allow the post_edited
webhook to have the correct topic values.

Original bug reported at:

https://meta.discourse.org/t/post-edited-webhook-does-not-reflect-updated-topic-title/144722

app/controllers/topics_controller.rb

@@ -366,7 +366,7 @@ class TopicsController < ApplicationController
 
     if changes.length > 0
       first_post = topic.ordered_posts.first
-      success = PostRevisor.new(first_post, topic).revise!(current_user, changes, validate_post: false)
+      success = PostRevisor.new(first_post).revise!(current_user, changes, validate_post: false)
     end
 
     # this is used to return the title to the client as it may have been changed by "TextCleaner"

spec/requests/topics_controller_spec.rb

@@ -946,6 +946,9 @@ RSpec.describe TopicsController do
       end
 
       describe 'with permission' do
+        fab!(:post_hook) { Fabricate(:post_web_hook) }
+        fab!(:topic_hook) { Fabricate(:topic_web_hook) }
+
         it 'succeeds' do
           put "/t/#{topic.slug}/#{topic.id}.json"
 
@@ -971,6 +974,13 @@ RSpec.describe TopicsController do
 
           topic.reload
           expect(topic.title).to eq('This is a new title for the topic')
+
+          expect(Jobs::EmitWebHookEvent.jobs.length).to eq(2)
+          job_args = Jobs::EmitWebHookEvent.jobs[0]["args"].first
+
+          expect(job_args["event_name"]).to eq("post_edited")
+          payload = JSON.parse(job_args["payload"])
+          expect(payload["topic_title"]).to eq('This is a new title for the topic')
         end
 
         it "returns errors with invalid titles" do