When traversing windows save the fact that windows above the topmost fullscreen window do not hide the lockscreen. If there is such a window don't show it. (cherry picked from commit ab55e524b89c13082193940a5bf8480a2c2522d9) Fixes bug 13225149. Change-Id: Ib6f33cbcfb2f60d8957a9184729ecdec80c6a236