Stabilize WebEngineViewLoadUrl::test_stopStatus

After stopping the load the active URL should be the url of the previous
successful load. Test active URL properly to make the test independent
from the previously executed test.

Change-Id: I53800fe28a722a5f3554b1ff2d4fc31cb8638dfd
Reviewed-by: Jüri Valdmann <juri.valdmann@qt.io>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>