Fix issue where padding is sent before media with undefined timestamps if not abs-send-time is enabled.

This broke bandwidth estimation for calls without abs-send-time is enabled, but where RTX was.

BUG=
R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/16929004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@6719 4adac7df-926f-26a2-2b94-8c16560cd09d
5 files changed