[OXUIB-304] Not possible to save drafts if ui/mail/replyTo/configurable is set to true
Bug notes
After mail compose is successfully loaded the values of all recipient tokenfields are read out (initially all are []) and the respective attributes are set in the model. If a difference is detected a request is sent.
The default values for to/cc/bcc are empty arrays [], so there is no difference detected.
The problem with the reply_to field is that since there is no default value for reply_to but the read out value is an empty array [], a difference is detected when setting the model and a request is sent - resulting in the error from the bug description.
This fix is only temporary and was not tested yet. Another solution is probably needed.