Fix bug: clean up the camera by adding .release()

Author: shaikmoeed

modules/optflow/samples/motempl.py

@@ -92,4 +92,6 @@ def draw_motion_comp(vis, rect, angle, color):
         prev_frame = frame.copy()
         if 0xFF & cv.waitKey(5) == 27:
             break
+    # cleanup the camera and close any open windows
+    cam.release()
     cv.destroyAllWindows()