AudioRecord: Add setLogSessionId

Update AudioTrack::setLogSessionId to match.

Test: atest AudioRecordTest#testSetLogSessionId
Test: atest AudioTrackTest#testSetLogSessionId
Test: adb shell dumpsys media.metrics
Bug: 181271535
Change-Id: I9754ce222a4723cf9b10a03db4e769cef6f3e93a
diff --git a/media/libaudioclient/AudioTrack.cpp b/media/libaudioclient/AudioTrack.cpp
index b7ba30d..d2f714a 100644
--- a/media/libaudioclient/AudioTrack.cpp
+++ b/media/libaudioclient/AudioTrack.cpp
@@ -3269,6 +3269,7 @@
 void AudioTrack::setLogSessionId(const char *logSessionId)
 {
      AutoMutex lock(mLock);
+    if (logSessionId == nullptr) logSessionId = "";  // an empty string is an unset session id.
     if (mLogSessionId == logSessionId) return;
 
      mLogSessionId = logSessionId;