Resolves crash in AudioTrack.flush() on Android.

BUG=b/65286737

Review-Url: https://codereview.webrtc.org/3010973002
Cr-Original-Commit-Position: refs/heads/master@{#19706}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 789825c42d2d93763b7d54454cd46e502c037592
1 file changed