Fix LinkCrawlWorker crashing on null created_at (#26151)

app/lib/link_details_extractor.rb

@@ -124,7 +124,7 @@ class LinkDetailsExtractor
       author_url: author_url || '',
       embed_url: embed_url || '',
       language: language,
-      created_at: published_at,
+      created_at: published_at.presence || Time.now.utc,
     }
   end