Keyguard: fix NPE setting lockscreen wallpaper

After boot the view might not be laid out and so getWidth() and
getHeight() return 0 and will cause a NullPointerException in
createBitmap().

Change-Id: Ibacf4199a69709dc34d21695732c2a5360533a23
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>
Themes: Use first asset entry for lockscreen wallpaper

The current implementation assumes the wallpaper will be named
either wallpaper.png or wallpaper.jpg.  If this is not the case
the wallpaper is not applied.  This patch implements the lockscreen
wallpaper the same way that the regular wallpaper is done.

Change-Id: I9f3dd299c1e61158fa53c163f7e42e21e2f9b1dc
Themes: Use default_wallpaper for HOLO lockscreen wp

Change-Id: I9c7fd29c99d13e811993eb9b3b045010431ccad0