[qwutils] insert_slice_clone can double drop if Clone panics.

An issue was discovered in the qwutils crate before 0.3.1 for Rust. When a Clone panic occurs, insert_slice_clone can perform a double drop.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-26954
• https://rustsec.org/advisories/RUSTSEC-2021-0018.html
• https://github.com/qwertz19281/rust_utils/issues/3
• https://github.com/advisories/GHSA-68p4-pjpf-xwcq