[clang] [CIR] Fix incorrect ConstArrayAttr trailing_zeros parsing (PR #188742)

[via cfe-commits]

NotLebedev wrote:

Added `clang/test/CIR/IR/string-trailing-zeros.cir`. Essentially checks `cir.global` declaration for the following two cases:
```c
char *a = "qwe";
char b[100] = "qwe";
```
Without the patch fails due to cir-opt crash. With patch works fine.

https://github.com/llvm/llvm-project/pull/188742