[clang] [analyzer] Fix crash in CStringChecker on zero-size element types (PR #191061)

[Donát Nagy via cfe-commits]

https://github.com/NagyDonat approved this pull request.

LGTM, but also let @steakhal react if he has opinion (e.g. about the `if !defined(_WIN32)` solution -- I think it's nice but I didn't see precedent for using this sort of thing instead of target triple pinning).

https://github.com/llvm/llvm-project/pull/191061