[clang] [clang-format] Fix crash involving array designators (PR #77045)

[via cfe-commits]

XDeme wrote:

> > While I was trying to find a minimal reproducer to the bug, I accidentally found that this patch fix another crash, and doesn't fix the linked issue.
> 
> Can you open another pull request to [fix](https://github.com/llvm/llvm-project/pull/77045#discussion_r1442578220) the other crash?

@owenca Just created #77723

https://github.com/llvm/llvm-project/pull/77045