Fail  tst_qdeclarativeborderimage::mirror() on Windows.

As expected. The test was using an invalid URL and thus
successfully comparing 2 empty images.

Task-number: QTBUG-32661
Change-Id: If6f0ad23454673b4b4fb2bc0a73da2b50663f171
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>