Merge pull request #23612 from cpoerschke:3.4-issue-21532

QRCodeDetector: don't floodFill with outside-of-image seedPoint #23612

Fixes #21532.

### Pull Request Readiness Checklist

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- [X] I agree to contribute to the project under Apache 2 License.
- [X] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [X] The PR is proposed to the proper branch
- [X] There is a reference to the original bug report and related work
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/objdetect/src/qrcode.cpp

@@ -570,10 +570,11 @@ bool QRDetect::computeTransformationPoints()
     {
         Mat mask = Mat::zeros(bin_barcode.rows + 2, bin_barcode.cols + 2, CV_8UC1);
         uint8_t next_pixel, future_pixel = 255;
-        int count_test_lines = 0, index = cvRound(localization_points[i].x);
-        for (; index < bin_barcode.cols - 1; index++)
+        int count_test_lines = 0, index_c = max(0, min(cvRound(localization_points[i].x), bin_barcode.cols - 1));
+        const int index_r = max(0, min(cvRound(localization_points[i].y), bin_barcode.rows - 1));
+        for (; index_c < bin_barcode.cols - 1; index_c++)
         {
-            next_pixel = bin_barcode.ptr<uint8_t>(cvRound(localization_points[i].y))[index + 1];
+            next_pixel = bin_barcode.ptr<uint8_t>(index_r)[index_c + 1];
             if (next_pixel == future_pixel)
             {
                 future_pixel = static_cast<uint8_t>(~future_pixel);
@@ -581,7 +582,7 @@ bool QRDetect::computeTransformationPoints()
                 if (count_test_lines == 2)
                 {
                     floodFill(bin_barcode, mask,
-                              Point(index + 1, cvRound(localization_points[i].y)), 255,
+                              Point(index_c + 1, index_r), 255,
                               0, Scalar(), Scalar(), FLOODFILL_MASK_ONLY);
                     break;
                 }