[clang] [clang] Fix a use-after-free in expression evaluation (PR #118480)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

Thanks! You're right, it may not address the issue we were seeing. Some of our were also ending up with:
```
==3187048==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x00001f73c115 in clang::APValue::operator=(clang::APValue&&) (/netbatch/donb2642835_00/runDir/dir/workspace/NIT/xmain/LX/xmainefi2linux_msan/ws/icsws/builds/xmainefi2linux_sprodusingprod/llvm/bin/clang-21+0x1f73c115)
```


https://github.com/llvm/llvm-project/pull/118480