Avoid clearing HaarEvaluator::tofs variable (introduced fb8478eb7b6c76f15c106c29a8843...

Avoid clearing HaarEvaluator::tofs variable (introduced fb8478eb7b6c76f15c106c29a8843d8c3722bb62) in HaarEvaluator::setImage(...) since it won't be recomputed by HaarEvaluator::computeOptFeatures() for cases where the input image dimensions and requested search scales are the same as the previous.  If none of the above change then it should be correct, and if they do change it will be computed correctly inside HaarEvaluator::computeOptFeatures() (in commit 952f9dbe629e8e9f310c70c78ed46d484439c1c9)

I'm guessing there is a unit test for this that needs to be called 2x with the same image and search parameters (or another image with the same size) to illustrate the problem.