[clang] [analyzer] Fix crash in PaddingChecker on dependent field types (PR #232986)

[Manuel Sainz de Baranda y Goñi via cfe-commits]

redcode wrote:

IMHO, it would be better if the PR that fixes the Sema bug added the assert to `PaddingChecker::shouldSkipDecl`. That way, neither PR would be blocked by a CI failure.

https://github.com/llvm/llvm-project/pull/232986