Deactive "sort by subject" of roundcube

In roundcube webmail client when you click on "subject" column, it will sort all your mails by subject! I don't know if it's useful or not but many times occured that I uncounsioucly clicked on this and it took long time to sort all messages by subject! Here's how to deactivate column sorting by subject :
- Open file : program/steps/mail/func.inc
- Search for "./#sort", for me it's around line 443. Then replace :
'onclick' => 'return '.JS_OBJECT_NAME.".command('sort','".$col."',this)
with :
'onclick' => 'return true'

That's it!