Fix race condition in RTPSEnder.

In RTPSender::SendPayloadType(), payload_type_ should not be read
without owning send_critsect_.

BUG=
R=pbos@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/8199004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5778 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed