Update imgwarp.cpp

Check for identity resize => use copy instead (1.37 ms -> 0.07 ms on 720p)

modules/imgproc/src/imgwarp.cpp

@@ -3257,6 +3257,12 @@ void cv::resize( InputArray _src, OutputArray _dst, Size dsize,
     Mat src = _src.getMat();
     _dst.create(dsize, src.type());
     Mat dst = _dst.getMat();
+    
+    if (dsize == ssize) {
+      // Source and destination are of same size. Use simple copy.
+      src.copyTo(dst);
+      return;
+    }
 
 #ifdef HAVE_TEGRA_OPTIMIZATION
     if (tegra::useTegra() && tegra::resize(src, dst, (float)inv_scale_x, (float)inv_scale_y, interpolation))