Fix for a potential data race condition

modules/objdetect/src/detection_based_tracker.cpp

@@ -284,7 +284,9 @@ void* cv::workcycleObjectDetectorFunction(void* p)
 {
     CATCH_ALL_AND_LOG({ ((cv::DetectionBasedTracker::SeparateDetectionWork*)p)->workcycleObjectDetector(); });
     try{
+        ((cv::DetectionBasedTracker::SeparateDetectionWork*)p)->lock();
         ((cv::DetectionBasedTracker::SeparateDetectionWork*)p)->stateThread = cv::DetectionBasedTracker::SeparateDetectionWork::STATE_THREAD_STOPPED;
+        ((cv::DetectionBasedTracker::SeparateDetectionWork*)p)->unlock();
     } catch(...) {
         LOGE0("DetectionBasedTracker: workcycleObjectDetectorFunction: ERROR concerning pointer, received as the function parameter");
     }