Fix a flicker when returning to the lockscreen

If we return to the lockscreen from a FLAG_SHOW_WHEN_LOCKED activity,
there was an additional black flicker as the wallpaper wasn't shown
for a couple of frames. The issue is that we didn't set the wallpaper
flag again, to fix another flicker with lockscreen wallpapers. Now,
we pass the state whether we currently have a lockscreen wallpaper
and if we don't have one, we immediately set the wallpaper flag
again.

Bug: 30829255
Bug: 30883413
Change-Id: I9faeaa77b98eb02058171ce19cf90b43826ebe9e