stylistic improvement

src/tracker.cpp

@@ -1186,8 +1186,9 @@ size_t Tracker::calcPrevFeaturePoints(int prevFrame, cv::Rect &rect, int frame,
                 continue;
             }
 
-            cv::Point2f p2f(at(i).at(prevFrame-at(i).firstFrame()).x()+borderSize,
-                        at(i).at(prevFrame-at(i).firstFrame()).y()+borderSize);
+            Vec2F prevPoint = at(i).at(prevFrame-at(i).firstFrame());
+            prevPoint += Vec2F(borderSize, borderSize);
+            cv::Point2f p2f = prevPoint.toCvPoint();
             if(rect.contains(p2f))
             {
                 mPrevFeaturePoints.push_back(p2f);