Merge "Update wallpaper offset when changing target from null" into sc-dev am: ccdb3242 am: ba8979c6 am: ac869af6 am: b3109e57

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

Change-Id: Iaaa76c953123ecf96685d272d6a5a48223ee32ca