Fix: Potential Vulnerability in Cloned Function

[tabudz]

Description
This PR fixes a security vulnerability in singlevar() that was cloned from lua but did not receive the security patch. The original issue was reported and fixed under lua/lua@1f3c6f4.
This PR applies the same patch to eliminate the vulnerability.

References
https://nvd.nist.gov/vuln/detail/CVE-2022-28805
lua/lua@1f3c6f4

[tpwrules]

We are still on Lua 5.3.6. It does not have the <const> feature and the CVE indicates it is not vulnerable.

Do you have reason to suspect this will affect us?

[tabudz]

I ran a code clone detection tool and found that this function might be a clone of a vulnerable one in my database. Just wanted to give you a heads-up. If you're confident that your case isn't vulnerable, then it likely isn't. Thanks for the clarification! Closed the PR.

[IamPete1]

Thanks for the report, were safe on 5.3 for now.