Fix: error in the dimension used for computeMinMax

Instead of using the current dimension for which we just got a big span,
we were computing Min and Max for the previous dimension stored in cutfeat
(and using 0 instead of the dimension indice for the very first dimension
with "span > (1-eps)max_span")

modules/flann/include/opencv2/flann/kdtree_single_index.h

@@ -461,7 +461,7 @@ private:
             DistanceType span = bbox[i].high-bbox[i].low;
             if (span>(DistanceType)((1-EPS)*max_span)) {
                 ElementType min_elem, max_elem;
-                computeMinMax(ind, count, cutfeat, min_elem, max_elem);
+                computeMinMax(ind, count, (int)i, min_elem, max_elem);
                 DistanceType spread = (DistanceType)(max_elem-min_elem);
                 if (spread>max_spread) {
                     cutfeat = (int)i;