WMF: fixed compilation on Windows Vista.

We were using one function which is available only on Windows 7 (and
later). Replace it with Vista-compatible calls.

Task-number: QTBUG-32864
Change-Id: I77492a407330c3689dfbf8dc1180894cf7ca5f8d
Reviewed-by: Christian Stromme <christian.stromme@digia.com>