WindowAnimator : Check KEYGUARD_PANEL when deciding to show/hide window

By default, if blur is enabled we don't hide the window behind since we
want the user to see it. This is not true for when a KEYGUARD_PANEL is active
since we can't see anything behind it anyway. Only apply blur logic
if KEYGUARD_PANEL is not added.

CYNGNOS-2980

Change-Id: Icecae14455d6e68665bb688e3f6dc4ea9d74e88c