[clang] [NFC][Clang] Avoid potential null pointer dereferences in Sema::AddInitializerToDecl(). (PR #106235)

[Tom Honermann via cfe-commits]

tahonermann wrote:

See https://github.com/llvm/llvm-project/pull/94368 for a prior attempt to address this static analysis concern.

https://github.com/llvm/llvm-project/pull/106235