Add advisory for git2: buffer-created BlameHunk leads to null pointers

[DanielEScherzer]

Affected crate(s)

• git2

Links to upstream issue(s) or PR(s)

rust-lang/git2-rs#1253, rust-lang/git2-rs#1254

Severity

Low? Null pointer derefs

Checklist

• Advisory filename(s) starts with RUSTSEC-0000-0000 as the ID
• date field is set to the public disclosure date
• Contains a concise and descriptive title after advisory metadata
• Asked maintainer(s) if publishing an advisory is appropriate

[DanielEScherzer]

Date is set as the date of the PR to fix the issue being created

Filed pre-emptively with versions > 0.20.4, will update once a new version has been released

[djc]

[ ] Asked maintainer(s) if publishing an advisory is appropriate

Please get a maintainer to commit somewhere public.