Corrected access of null pointer in audioproc_f

webrtc/modules/audio_processing/test/aec_dump_based_simulator.cc

Index: webrtc/modules/audio_processing/test/aec_dump_based_simulator.cc
diff --git a/webrtc/modules/audio_processing/test/aec_dump_based_simulator.cc b/webrtc/modules/audio_processing/test/aec_dump_based_simulator.cc
index 10d4fcdf6f9ab4f44134728284a601d502b6202e..f444967a108955069df3002f0c934e108b83e09a 100644
--- a/webrtc/modules/audio_processing/test/aec_dump_based_simulator.cc
+++ b/webrtc/modules/audio_processing/test/aec_dump_based_simulator.cc
@@ -230,12 +230,11 @@ void AecDumpBasedSimulator::Process() {
         << "Only mono files for the artificial nearend are supported, "
            "reverted to not using the artificial nearend file";
 
+    const int sample_rate_hz = artificial_nearend_file->sample_rate();
     artificial_nearend_buffer_reader_.reset(
         new ChannelBufferWavReader(std::move(artificial_nearend_file)));
     artificial_nearend_buf_.reset(new ChannelBuffer<float>(
-        rtc::CheckedDivExact(artificial_nearend_file->sample_rate(),
-                             kChunksPerSecond),
-        1));
+        rtc::CheckedDivExact(sample_rate_hz, kChunksPerSecond), 1));

[ivoc, 2016/12/14 10:26:41]

Maybe I'm missing something, but to me it looks like this statement is exactly
the same (minus formatting) as before the change. How does this prevent access
of a nullptr?

[peah-webrtc, 2016/12/14 10:33:40]

I think what happens is that the pointer artificial_nearend_file is lost  in the
std::move() operation on row 235, which in turn makes the call to
artificial_nearend_file->sample_rate() access an invalid pointer.

But please correct me if I'm wrong in that and that something else was wrong.
The former code fails when I run it, and the new code does not fail.

[ivoc, 2016/12/14 10:37:06]

Ah right, that's a good point. It's easy to forget the effect of std::move (I
guess that's why it was missed in the initial CL).

   }
 
   webrtc::audioproc::Event event_msg;