We were failing the conditional that would point «str» to «buffW»
when retrieving the GEO_ISO_UN_NUMBER of a location with UN code 0.

Some locations will keep having no UN code, such as Guantanamo Bay or
Johnston Atoll, since that's how those are defined in Windows.
Signed-off-by: João Diogo Craveiro Ferreira <devilj@outlook.pt>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>