[clang] [Clang] Initialize AtLeastAsSpecialized to prevent undefined behavior in Sema::isTemplateTemplateParameterAtLeastAsSpecializedAs() (PR #95195)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

There is no potential UB, this is a false positive: this lambda will always be executed before runWithSufficientStackSpace returns.

https://github.com/llvm/llvm-project/pull/95195