Merge pull request #25771 from fengyuentau:vittrack_black_input

video: fix vittrack in the case where crop size grows until out-of-memory when the input is black #25771

Fixes https://github.com/opencv/opencv/issues/25760

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [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
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/video/test/test_trackers.cpp

@@ -166,9 +166,7 @@ TEST(vittrack, accuracy_vittrack)
     cv::TrackerVit::Params params;
     params.net = model;
     cv::Ptr<Tracker> tracker = TrackerVit::create(params);
-    // NOTE: Test threshold was reduced from 0.67 (libjpeg-turbo) to 0.66 (libjpeg 9f),
-    // becase libjpeg and libjpeg-turbo produce slightly different images
-    checkTrackingAccuracy(tracker, 0.66);
+    checkTrackingAccuracy(tracker, 0.64);
 }
 
 }}  // namespace opencv_test::