ntdll: add a warning about running wine as root (resend)

[Vincent Povirk]

> To abstract what you're saying here, you're suggesting to extend the
> wineprefix ownership test to include $HOME when $WINEPREFIX is not set
> and $HOME/.wine does not exist?
>
> That doesn't sounds like a bad idea to me. But I'm not so sure about
> specifically testing on UID=0 or SUDO_USER.
This specifically covers the one case that is broken for people who
maybe can't be expected to know any better: running wine for the first
time using sudo on ubuntu. I don't know why else $HOME would not be
owned by you, but I've been assuming we want Wine to function in those
cases (otherwise, we'd have added this test when we added the original
ownership test, right?).

If a user's home directory will always be owned by the user in a
working Unix-like configuration, there's no need to test uid or
SUDO_USER.