Protect from negative second moments, which are unexpected in TransientDetector::Detect and may lead to invalid results. Bug: chromium:866925 Change-Id: Id1d5b2ebb51e54d9d332b869c6f63dcd03cc461c Reviewed-on: https://webrtc-review.googlesource.com/91164 Commit-Queue: Alessio Bazzica <alessiob@webrtc.org> Reviewed-by: Sam Zackrisson <saza@webrtc.org> Cr-Commit-Position: refs/heads/master@{#24153}