This allows detecting if it has been set reliably. 0 is a valid payload type. Bug: webrtc:360058654 Change-Id: Ic3646abe20d0247592145ad27549fa46ddb7ec90 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/362261 Reviewed-by: Henrik Boström <hbos@webrtc.org> Commit-Queue: Harald Alvestrand <hta@webrtc.org> Cr-Commit-Position: refs/heads/main@{#43016}