Make BW checks > 0 in peerconnection_unittest.cc.
Make BW checks > 0 in peerconnection_unittest.cc.

These checks (> 40k) fail on LSan FYI bots and the purpose of them seem
to be that we're getting non-zero BW reported.

R=stefan@webrtc.org
TBR=jiayl@webrtc.org, solenberg@webrtc.org
BUG=3817,chromium:375154

Review URL: https://webrtc-codereview.appspot.com/29479004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 000d86792d6fb57948ce60b3a3e9c8f34768f46c

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