Fix first return value of FetchLinkCardService.html method (#15630)

app/services/fetch_link_card_service.rb

@@ -47,11 +47,11 @@ class FetchLinkCardService < BaseService
 
     Request.new(:get, @url).add_headers('Accept' => 'text/html', 'User-Agent' => Mastodon::Version.user_agent + ' Bot').perform do |res|
       if res.code == 200 && res.mime_type == 'text/html'
-        @html = res.body_with_limit
         @html_charset = res.charset
+        @html = res.body_with_limit
       else
-        @html = nil
         @html_charset = nil
+        @html = nil
       end
     end
   end