[clang] [alpha.webkit.UncountedLocalVarsChecker] Handle null Type in CanTriviallyDestruct (PR #182129)

[Ryosuke Niwa via cfe-commits]

rniwa wrote:

I've pushed another fix around `R->hasTrivialDestructor()`. We need to ensure that R has a definition before calling `hasTrivialDestructor`.

https://github.com/llvm/llvm-project/pull/182129