Undefined behavior in NvidiaOpticalFlowImpl_2

[cabranca]

System information (version)

• OpenCV => 4.12
• Operating System / Platform => Ubuntu 22.04
• Compiler => gcc 13.3

Detailed description

When calling NvidiaOpticalFlowImpl_2::calc with a scale factor of 1 (grid size == hardware grid size), the program fails the assertion in GpuMat constructor when comparing the step and minStep.

After debugging I've found that as the scale factor equals 1, this variable is never initialized

But then it is used to construct the upscaled buffer.

Steps to reproduce

As it is an undefined behavior, I wasn't able to reproduce this with other machine other than mine.

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  forum.opencv.org, Stack Overflow, etc and have not found any solution
• I updated to the latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc