I don't see why it would be adding those line breaks. To debug I'd find the function:
protected function mailSend($header, $body)
and add this at the top:
die($body);
That should show the actual body message being sent to your smtp server to deliver. If the line breaks are there, then you at least know it is something that is being added by the code and we can track it back. It's possible its being added by your smtp server or mail client.