This CL fixes the bug that we must have some padding for H264 codec when used in Multiplex encoder/decoder, otherwise H264 decoder will crash. And this CL fixes a bug that potential infinite loop exists in MultiplexEncoderAdapter Bug: webrtc:8921 Change-Id: I4124579c31ee69f72e29d118378aa1f8b3f05eb4 Reviewed-on: https://webrtc-review.googlesource.com/56960 Commit-Queue: Qiang Chen <qiangchen@chromium.org> Reviewed-by: Emircan Uysaler <emircan@webrtc.org> Cr-Commit-Position: refs/heads/master@{#22175}