ACM: Properly initialize last_audio_buffer_ array

Only half of the array was initialized. Now all of it is.

Bug: chromium:839960
Change-Id: If8bbe12c4c4c0dc0d529c93b22e49a94ecb09919
Reviewed-on: https://webrtc-review.googlesource.com/74820
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Henrik Lundin <henrik.lundin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23167}

modules/audio_coding/acm2/acm_receiver.cc

@@ -40,7 +40,8 @@ AcmReceiver::AcmReceiver(const AudioCodingModule::Config& config)
       clock_(config.clock),
       resampled_last_output_frame_(true) {
   RTC_DCHECK(clock_);
-  memset(last_audio_buffer_.get(), 0, AudioFrame::kMaxDataSizeSamples);
+  memset(last_audio_buffer_.get(), 0,
+         sizeof(int16_t) * AudioFrame::kMaxDataSizeSamples);
 }
 
 AcmReceiver::~AcmReceiver() = default;