DEV: Gracefully handle an array of IDs passed to Topics#show (#28631)

We're seeing a lot of log noise coming from unhandled exceptions stemming from requests to TopicsController#show where id is passed in as an array.

In the implementation of the method, we assume that if id is present it will be a string. This is because one of the routes to this action uses :id as a URL fragment, and so must be a string. However, there are other routes that go to this endpoint as well. Some of them don't have this URL fragment, so you can pass an arbitrary id query parameter.

Instead of a downstream unhandled exception, we raise a Discourse::InvalidParameters upfront.

app/controllers/topics_controller.rb

@@ -51,6 +51,10 @@ class TopicsController < ApplicationController
   end
 
   def show
+    if params[:id].is_a?(Array)
+      raise Discourse::InvalidParameters.new("Show only accepts a single ID")
+    end
+
     flash["referer"] ||= request.referer[0..255] if request.referer
 
     # TODO: We'd like to migrate the wordpress feed to another url. This keeps up backwards