Prevent zero division in VCMJitterEstimator.
Prevent zero division in VCMJitterEstimator.

BUG=webrtc:5124
R=sprang@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/1652903002 .

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#11445}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 74451a5ea97a1f8f30acba142d829728813bb0a7

Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,Alkalyne/webrtctrunk,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc