In calcOpticalFlowSF, fixed several uninitialized uses of matrices.
In calcOpticalFlowSF, fixed several uninitialized uses of matrices.

This should fix that pesky test failure that pops up from time to time.

I don't actually know if the default values should be zeros, but the tests
pass, so...

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