condition custom replyTo option correction

the custom replyto option for civimail is configured in mailing settings.
but in our form construction, we only condition the field existence using isset. we should be using isset + !empty. with the current condition, if you change the value on then off, and return to the mailing form, the reply to field persists because the array key still exists in the config object.

https://fisheye2.atlassian.com/browse/CiviCRM/trunk/CRM/Mailing/Form/Upload.php?hb=true
line 234. we should have:
if ( isset($config->replyTo) && !empty($config->replyTo) && ! CRM_Utils_Array::value( 'override_verp', $options ) ) {