[CRD iOS] Fix empty closure crash in AudioStreamConsumer::ProcessAudioPacket

WebRTCAudioSinkAdapter passes an empty done closure to AudioStreamConsumer.
Different from a DoNothing closure, calling an empty closure will end up
crashing the app. This CL fixes AudioStreamConsumer so that it only runs
the done closure if it is not null.

Bug: 748710
Change-Id: Ied6301b54e694f8d62618e7ed4e16fa2811a4202
Reviewed-on: https://chromium-review.googlesource.com/765010
Reviewed-by: Jamie Walch <[email protected]>
Commit-Queue: Yuwei Huang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#515771}
1 file changed