[clang] [clang][bytecode] Fix null Descriptor dereference in ArrayElemPtrPop (PR #163386)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

Thank you for the fix, since no one mentioned it in the review, it looks like Timm took care of it when he merged but I wanted to mention it to you for the future.

The summary is normally what goes into the git log and so what is there should cover

- A description of the problem
- A description of the solution 
- A description of other important details like specific algorithms or design choices

Any questions should be made as comments to the PR and they can be addressed as replies.

https://github.com/llvm/llvm-project/pull/163386