[Bug 57338] wine-gecko/wine-mono don't cache their installers if using a username with unicode characters

[WineHQ Bugzilla]

https://bugs.winehq.org/show_bug.cgi?id=57338

--- Comment #2 from Esme Povirk  ---
Saw this error in a log:

0164:warn:appwizcpl:get_cache_file_name L"Z:\home\t\fffdstuser\.cache" does
not exist and could not be created (3)

I think we lost the unicode character when doing getenv() here:
https://gitlab.winehq.org/wine/wine/-/blob/master/dlls/appwiz.cpl/addons.c?r...

Checking in cmd, both XDG_CACHE_HOME and WINEHOMEDIR preserve the character,
and WINEHOMEDIR is set to ??\Z:\home\tëstuser, so clearly this conversion from
a unix path to dos path is possible, but I'm not sure how to do it properly.