Since the address of the dereference is taken this inputs a garbage
almost-null pointer into RtpPacketizer. Not likely that a load/store is
performed on the address, but UBSan fires and it's a source of potential
future errors.
BUG=webrtc:5124, webrtc:5490
R=stefan@webrtc.org
Review URL: https://codereview.webrtc.org/1677003002 .
Cr-Commit-Position: refs/heads/master@{#11528}