Fix kotlin nullable errors in Launcher3 am: 4cc251e6c1

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Launcher3/+/24406718

Change-Id: Id52bac704d54d31eafda8c8b648a576ab56617c8
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>