issue with getAverageFlowInRegion about opencv-processing

[b2renger]

Ok I got it !

this is actually due to the fact that I tried to get a portion of image that was partly out of range.

for (int i = 0; i < cam.width - steps; i += steps) {
      for (int j = 0; j < cam.height- steps; j += steps) {
        PVector p = (opencv.getAverageFlowInRegion(int(i), int(j), steps, steps));
        float red = p.mag();
        fill(red, 0, 0);
        rect(i, j, 10, 10);
      }
    }