QLocale::nativeLanguageName can return empty strings

On Windows for some of the more exotic locales like "nds" (Low German) nativeLanguageName returns an Empty string.

This is unexpected and is not mentioned in the the documentation.
https://doc.qt.io/qt-5/qlocale.html#nativeLanguageName

Ideally there would be some kind of fallback for the names where getLocaleInfo(LOCALE_SNATIVELANGUAGENAME) returns an empty string. At least it should be mentioned in the Documentation.

(Affects Version 5.5.1 chosen because that's the one I've tested but probably true for newer versions, too)

See https://git.reviewboard.kde.org/r/127136 for an example why this can be problematic.