Fix three uninitialized members in rtp_receiver_impl.cc.

R=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/1781004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@4320 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed