Fixes #7603, which was caused by OCVViewPort::icvmouseProcessing
not being declared as virtual, and hence was not overriden by
DefaultViewPort::icvmouseProcessing (which does the inverse
coordinate mapping).

  * vget_lane_** accepts constant value, not variable

modules/objectdetect/src/detection_based_tracker.cpp: made unique_lock<mutex> local to each function
samples/cpp/dbt_face_detection.cpp: fixed warnings on loop in Visual Studio