[clang] [clang][bytecode] Diagnose dereferencing a null pointer (PR #149330)

[Corentin Jabot via cfe-commits]

https://github.com/cor3ntin approved this pull request.

LGTM, thanks.
(Note that this does not cover the case of forming a reference to a one-past-the-end object, which is covered by the same wording, but if you don't already do that, it can be a separate pr.

https://github.com/llvm/llvm-project/pull/149330