Fixing a bug in DummyRTPpacket

This bug caused writing outside allocated memory when RTP header
extensions were used.

BUG=2834
TBR=turaj@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/8009005

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5489 4adac7df-926f-26a2-2b94-8c16560cd09d
3 files changed