Use original URL in preview if it redirects to 4xx page (#26200)

app/services/fetch_link_card_service.rb

@@ -45,20 +45,18 @@ def process_url
   def html
     return @html if defined?(@html)
 
-    Request.new(:get, @url).add_headers('Accept' => 'text/html', 'User-Agent' => "#{Mastodon::Version.user_agent} Bot").perform do |res|
+    @html = Request.new(:get, @url).add_headers('Accept' => 'text/html', 'User-Agent' => "#{Mastodon::Version.user_agent} Bot").perform do |res|
+      next unless res.code == 200 && res.mime_type == 'text/html'
+
       # We follow redirects, and ideally we want to save the preview card for
       # the destination URL and not any link shortener in-between, so here
       # we set the URL to the one of the last response in the redirect chain
       @url  = res.request.uri.to_s
       @card = PreviewCard.find_or_initialize_by(url: @url) if @card.url != @url
 
-      if res.code == 200 && res.mime_type == 'text/html'
-        @html_charset = res.charset
-        @html = res.body_with_limit
-      else
-        @html_charset = nil
-        @html = nil
-      end
+      @html_charset = res.charset
+
+      res.body_with_limit
     end
   end