[clang] [clang][CodeGen] Fix size calculation in vbptr split memory region in EmitNullBaseClassInitialization (PR #184558)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic approved this pull request.

LGTM

Note GitHub has special support if you write exactly "Fixes #42101" in the commit message: it closes the bug for you.

https://github.com/llvm/llvm-project/pull/184558