[clang-tools-extra] [clang-tidy] Fix crashes when analyzing unknown exceptions in bugprone-exception-escape (PR #218067)

[Zeyi Xu via cfe-commits]

zeyi2 wrote:

> Maybe we can also run all values of `TreatFunctionsWithoutSpecificationAsThrowing` against main `exception-escape.cpp` test suite? I think that would reveal the early bug probably?

That makes sense. I tried all three values against exception-escape.cpp locally, and they did not uncover any additional issues. Given that the diff is quite large and it is not a correctness blocker, I'd like to open a separate NFC follow-up for it. WDYT?

https://github.com/llvm/llvm-project/pull/218067