[clang] [clang][BufferUsage] Fix crash when parsing invalid format string (PR #170496)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for working on this! It should also come with a release note in `clang/docs/ReleaseNotes.rst` so users know about the fix.

https://github.com/llvm/llvm-project/pull/170496