Fix accessing uninitialized variables when not processing a reverse stream.
Fix accessing uninitialized variables when not processing a reverse stream.

TBR=turaj@webrtc.org

Review URL: https://codereview.webrtc.org/1306863003 .

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#9758}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: c0775c02910c14743cc46fbd4618de1b20ecc681

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