intl: Fix the Windows MUI code, so that it works on Windows 10.
Reported by <lrn1986@gmail.com> at <https://savannah.gnu.org/bugs/?65128>.
* gettext-runtime/intl/langprefs.c (_nl_language_preferences_win32_mui): Make
GetUserPreferredUILanguages prototype with Microsoft's current documentation.
Allow the first GetUserPreferredUILanguages call to succeed.
