Audioflinger: Do not intercept if no audio

This was not efficient and leaded to an assert in obtainBuffer.
I'm not sure which condition can lead to a getNextBuffer of size 0,
but it has been observed and is not forbidden by getNextBuffer
documentation.

Test: atest android.media.cts.AudioPlaybackCaptureTest#testCaptureMediaUsage
Bug: 111453086
Change-Id: I5accf7c1d488ff4686272588329bab71d64f67cd
Signed-off-by: Kevin Rocard <krocard@google.com>
diff --git a/services/audioflinger/Tracks.cpp b/services/audioflinger/Tracks.cpp
index 65f799e..ad78a45 100644
--- a/services/audioflinger/Tracks.cpp
+++ b/services/audioflinger/Tracks.cpp
@@ -700,8 +700,13 @@
         const AudioBufferProvider::Buffer& sourceBuffer) {
     auto start = std::chrono::steady_clock::now();
     const size_t frameCount = sourceBuffer.frameCount;
-    for (auto& sink : mTeePatches) {
-        RecordThread::PatchRecord* patchRecord = sink.patchRecord.get();
+    if (frameCount == 0) {
+        return;  // No audio to intercept.
+        // Additionally PatchProxyBufferProvider::obtainBuffer (called by PathTrack::getNextBuffer)
+        // does not allow 0 frame size request contrary to getNextBuffer
+    }
+    for (auto& teePatch : mTeePatches) {
+        RecordThread::PatchRecord* patchRecord = teePatch.patchRecord.get();
 
         size_t framesWritten = writeFrames(patchRecord, sourceBuffer.i8, frameCount);
         // On buffer wrap, the buffer frame count will be less than requested,