DEV: Make find_post_using raise only Discourse::NotFound (#16133)

app/controllers/posts_controller.rb

@@ -869,7 +869,7 @@ class PostsController < ApplicationController
     post = finder.with_deleted.first
     raise Discourse::NotFound unless post
 
-    post.topic = Topic.with_deleted.find(post.topic_id)
+    post.topic = Topic.with_deleted.find_by(id: post.topic_id)
 
     if !post.topic ||
        (

spec/requests/posts_controller_spec.rb

@@ -16,6 +16,12 @@ shared_examples 'finding and showing post' do
     expect(response.status).to eq(200)
   end
 
+  it "returns 404 when post's topic is deleted" do
+    post.topic.destroy!
+    get url
+    expect(response.status).to eq(404)
+  end
+
   context "deleted post" do
     before do
       post.trash!(user)