GetInputPin() and GetOutputPin() do not guarantee returning non-null pins. Should either of them return null during Init() we're better off returning an error than allowing unsafe behavior further ahead. Bug: webrtc:9941 Change-Id: I25858f0555334b4ef99801f83454931384695bf6 Reviewed-on: https://webrtc-review.googlesource.com/c/108603 Reviewed-by: Per Kjellander <perkj@webrtc.org> Commit-Queue: Per Kjellander <perkj@webrtc.org> Cr-Commit-Position: refs/heads/master@{#25475}