fix overflow issue when computing diagonal

- with big images the int multiplication can overflow

modules/xfeatures2d/src/sift.cpp

@@ -579,7 +579,7 @@ static void calcSIFTDescriptor( const Mat& img, Point2f ptf, float ori, float sc
     float hist_width = SIFT_DESCR_SCL_FCTR * scl;
     int radius = cvRound(hist_width * 1.4142135623730951f * (d + 1) * 0.5f);
     // Clip the radius to the diagonal of the image to avoid autobuffer too large exception
-    radius = std::min(radius, (int) sqrt((double) img.cols*img.cols + img.rows*img.rows));
+    radius = std::min(radius, (int) sqrt(((double) img.cols)*img.cols + ((double) img.rows)*img.rows));
     cos_t /= hist_width;
     sin_t /= hist_width;