Fix reporting of time_between_freezes_ms when all peers were unregistered before end of the call. Bug: b/243501613 Change-Id: Ie2b77d8399e4f4bf672e80f62ed27609336af171 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/272650 Reviewed-by: Andrey Logvin <landrey@google.com> Commit-Queue: Artem Titov <titovartem@webrtc.org> Cr-Commit-Position: refs/heads/main@{#37885}