fix: fix slice init length

[cuishuang]

What type of PR is this?

Bug fix

What does this PR do? Why is it needed?

The intention here should be to initialize a slice with a capacity of 32-len(numBytes) rather than initializing the length of this slice.

The only demo: https://go.dev/play/p/q1BcVCmvidW

Which issues(s) does this PR fix?

Fixes #

Other notes for review

Acknowledgements

• [x] I have read CONTRIBUTING.md.
• [ ] I have made an appropriate entry to CHANGELOG.md.
• [ ] I have added a description to this PR with sufficient context for reviewers to understand this PR.

[CLAassistant]

All committers have signed the CLA.

[prestonvanloon]

I think you are mistaken. The desired behavior is to pad the slice with zeros, not just allocating a capacity on the slice.