Merge "Update wallpaper offset when changing target from null" into sc-dev am: ccdb324274 am: a1d274c92a am: 04a301b6de

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/15521640

Change-Id: Ic1cde13ed66474684d1f8d65e1d453405dd47d67