fix(wechat_qrcode): fixed memory leaks

[Konano]

Pull Request Readiness Checklist

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

• I agree to contribute to the project under Apache 2 License.
• 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
• The PR is proposed to the proper branch
• 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

[opencv-alalek]

LGTM 👍 Thank you for the fix!

BTW, manual memory management through new/delete or malloc/free should be avoided.
cv::AutoBuffer or std::vector should be used instead.

[n0099]

Marked as CVE-2023-2618