msvcrt.getch() returns EOF sentinel as data when no console is attached

Bug report

Bug description:

"msvcrt.getch() returns EOF sentinel as data when no console is attached" --body "## Summary

On Windows, `msvcrt.getch()` returns the CRT EOF sentinel as normal Python data when no console is attached, instead of raising `OSError`.

Reproducer

```powershell
PCbuild\amd64\python_d.exe -c "import ctypes, msvcrt, sys; ctypes.windll.kernel32.FreeConsole(); sys.exit(0 if msvcrt.getch() == b'\xff' else 1)"
echo $LASTEXITCODE \``

Actual result:
`$LASTEXITCODE` is `0`

This means `msvcrt.getch()` returned `b'\xff'` after `FreeConsole()`.

Expected behavior

If `_getch()` fails because no console is attached, the Python wrapper should raise `OSError` instead of returning `b'\xff'`.

Environment

• OS: Windows 11
• Build: CPython debug build
• Command used to build: `PCbuild\build.bat -c Debug`"

CPython versions tested on:

3.15

Operating systems tested on:

Windows

Linked PRs

• gh-149450

從 msvcrt.getch() 進入點開始，並在 FreeConsole() 之後使用 PCbuild/amd64/python_d.exe 命令重現該行為。確認缺少主控台時不再產生 b'\xff'，而是改為引發 OSError；issue 列出了連結的 PR gh-149450，因此請先檢查該工作。