[clang] [CIR] Make sure ptr-cast-to-vbase is guarded. (PR #225969)

[Andy Kaylor via cfe-commits]

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

lgtm

The null check for non-virtual base and derived class address is folded into the operation in CIR, but in the virtual base class case we dipped into the CXXABI early to do the calculations during codegen. I guess the null check got lost in the mixing of models for how to handle this.

https://github.com/llvm/llvm-project/pull/225969