Update thinning.cpp

Author: sturkmen72

modules/ximgproc/src/thinning.cpp

@@ -125,10 +125,11 @@ static void thinningIteration(Mat &img, Mat &marker, const uint8_t* const lut) {
 
 // Apply the thinning procedure to a given image
 void thinning(InputArray input, OutputArray output, int thinningType){
-    Mat processed = input.getMat().clone();
-    CV_CheckTypeEQ(processed.type(), CV_8UC1, "");
-    // Enforce the range of the input image to be in between 0 - 255
-    processed /= 255;
+    Mat input_ = input.getMat();
+    CV_Assert(!input_.empty());
+    CV_CheckTypeEQ(input_.type(), CV_8UC1, "");
+
+    Mat processed = input_ / 255;
     Mat prev = processed.clone();
 
     Mat marker,marker_inner = processed(Rect(1, 1, processed.cols - 2, processed.rows - 2));