Clear the timestamp latch valid flag if no new timestamp available

Bug: 11815245
Change-Id: I94885a1b4c2c7c055b8eacc7f7d0fcd064094b6d
diff --git a/services/audioflinger/Threads.cpp b/services/audioflinger/Threads.cpp
index f721d5c..eb286ae 100644
--- a/services/audioflinger/Threads.cpp
+++ b/services/audioflinger/Threads.cpp
@@ -2132,6 +2132,7 @@
         } else {
             bytesWritten = framesWritten;
         }
+        mLatchDValid = false;
         status_t status = mNormalSink->getTimestamp(mLatchD.mTimestamp);
         if (status == NO_ERROR) {
             size_t totalFramesWritten = mNormalSink->framesWritten();