Merge "Update wallpaper offset when changing target from null" into sc-dev am: ccdb324274 am: ba8979c6d7 am: ac869af650

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

Change-Id: I1a02ea48890b092aadb0bdd18717f4477af0d1e3