added test for correct handling of uniforma areas in the MergeMertens
added test for correct handling of uniforma areas in the MergeMertens

apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,apavlenko/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv