FIX: Don't add a slug to constructed quote urls (#12052)

A topic with the slug 'topic' might exist and may end up being linked to
by mistake when malformed (i.e. cross-site) quotes are posted.

lib/pretty_text.rb

@@ -333,7 +333,7 @@ module PrettyText
     # extract quotes
     doc.css("aside.quote[data-topic]").each do |aside|
       if aside["data-topic"].present?
-        url = +"/t/topic/#{aside["data-topic"]}"
+        url = +"/t/#{aside["data-topic"]}"
         url << "/#{aside["data-post"]}" if aside["data-post"].present?
         links << DetectedLink.new(url, true)
       end