Clang Crash in LValue/ExprConstant on Malformed Array Initializer (trunk + assertion)

## Overview
- crash on invalid
- generated by fuzzer
- crashes both trunk and assertion builds

## Code
```c
arr[;
arr[];
void func(){
int* ptr = arr-1;
}
```

## CompilerExplorer
https://godbolt.org/z/fq5scf5d1

## Notes
- Thought this was related to #170072, but that does not crash the non-assertion trunk build, unlike this code.
- Here is the godbolt for that issue: https://godbolt.org/z/a1bnMahrn

Reproduce the crash with the malformed C initializer in the issue using the linked Compiler Explorer case, comparing trunk and assertion builds. Start by tracing the Clang LValue/ExprConstant path named in the title and inspect the related issue #170072 for context. Done means the reproducer no longer crashes in either build, with regression coverage for this input.

Written by the indexing model from the issue text.