Make sure to also check for null CFPropertyLists.

In 1b08e0307d, I removed the null check
by accident. It's possible for the Darwin API to return a null
property list.

Task-number: QTBUG-30760
Change-Id: Iaf0125767fe4b47c19810b70483a5219e94e4305
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>

src/corelib/tools/qlocale_mac.mm

@@ -438,6 +438,9 @@ QVariant QSystemLocale::query(QueryType type, QVariant in = QVariant()) const
                  kCFPreferencesCurrentUser,
                  kCFPreferencesAnyHost);
         QStringList result;
+        if (!languages)
+            return QVariant(result);
+
         CFTypeID typeId = CFGetTypeID(languages);
         if (typeId == CFArrayGetTypeID()) {
             const int cnt = CFArrayGetCount(languages.as<CFArrayRef>());