fixed roi handling in HOGDescriptor::computeGradient (ticket #295).
fixed roi handling in HOGDescriptor::computeGradient (ticket #295).

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