Do not crash with IA2 AT clients.

Make sure all members of the IA2Locale we return are properly
initialized. Only accProbe provoked this bug, and I have no idea why
this haven't crashed earlier.

nvda probably does not query the locale, therefore it was unaffected.

Change-Id: I5a9d98eed5af56fd2a75f6cb7035ed613fd802d5
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>

src/plugins/platforms/windows/accessible/iaccessible2.cpp

@@ -522,6 +522,7 @@ HRESULT STDMETHODCALLTYPE QWindowsIA2Accessible::get_locale(IA2Locale *locale)
     QLocale l;
     res.country = QStringToBSTR(QLocale::countryToString(l.country()));
     res.language = QStringToBSTR(QLocale::languageToString(l.language()));
+    res.variant = QStringToBSTR(QString());
     *locale = res;
     return S_OK;
 }