[clang] [clang][bytecode] Fix null ptr upcasts adding offset (PR #224873)

[Benji Smith via cfe-commits]

Benjins wrote:

Looks like the windows run was a networking timeout:
```
    File "C:\Python312\Lib\socket.py", line 707, in readinto
      return self._sock.recv_into(b)
             ^^^^^^^^^^^^^^^^^^^^^^^
  TimeoutError: timed out
```
I assume a transient issue, since the previous run passed and the only change here was the release notes update

https://github.com/llvm/llvm-project/pull/224873