Fix race condition for Cascade Classifier when TBB enabled.

modules/objdetect/src/cascadedetect.cpp

@@ -992,9 +992,9 @@ public:
                     {
                         mtx->lock();
                         rectangles->push_back(Rect(cvRound(x*scalingFactor), cvRound(y*scalingFactor), winSize.width, winSize.height));
-                        mtx->unlock();
                         rejectLevels->push_back(-result);
                         levelWeights->push_back(gypWeight);
+                        mtx->unlock();
                     }
                 }
                 else if( result > 0 )