[clang] [clang-format] Fix a crash on triple-bracket input like `[[[a]]` (PR #199103)

[Björn Schäpers via cfe-commits]

https://github.com/HazardyKnusperkeks commented:

For this and the other PRs, please read https://llvm.org/docs/AIToolPolicy.html

I'm fairly sure that this is AI generated.

https://github.com/llvm/llvm-project/pull/199103