fixed single-mat input/output in mixChannels() (ticket #1446)
fixed single-mat input/output in mixChannels() (ticket #1446)

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