libcamera: avoid a race condition on starting and stopping a recording

precondition: preview is running
-- call startRecording()
-- a preview frame arrives, causing the record callback to be called, and then
   blocks on mRecordWait.wait()
-- call stopRecording(), which sets mReleasedRecordingFrame and signals
   mRecordWait;
-- call startRecording(), which clears mReleasedRecordingFrame;
-- receivePreviewFrame() wakes up, checks mReleasedRecordingFrame, and
   blocks again on mRecordWait.wait(), without having notified the client.

Signed-off-by: Iliyan Malchev <malchev@google.com>

libcamera2/QualcommCameraHardware.cpp

@@ -1547,7 +1547,7 @@ void QualcommCameraHardware::receivePreviewFrame(struct msm_frame *frame)
     if(rcb != NULL) {
         Mutex::Autolock rLock(&mRecordFrameLock);
         rcb(mPreviewHeap->mBuffers[mPreviewFrameOffset], rdata);
-        while(mReleasedRecordingFrame != true) {
+        if (mReleasedRecordingFrame != true) {
             LOGV("block for release frame request/command");
             mRecordWait.wait(mRecordFrameLock);
         }