QStandardPaths::standardLocations()/WinRT: Return empty lists.

Previously, lists containing one empty string were returned for the
unimplemented functions.

Change-Id: Ia64b53325420e32076f2bacf22c48885d7121df0
Reviewed-by: Maurice Kalinowski <maurice.kalinowski@theqtcompany.com>

src/corelib/io/qstandardpaths_winrt.cpp

@@ -123,7 +123,8 @@ QString QStandardPaths::writableLocation(StandardLocation type)
 
 QStringList QStandardPaths::standardLocations(StandardLocation type)
 {
-    return QStringList(writableLocation(type));
+    const QString writable = writableLocation(type);
+    return writable.isEmpty() ? QStringList() : QStringList(writable);
 }
 
 QT_END_NAMESPACE