Merge "Add null pointer check for callback in HotwordDetectionConnection." into sc-dev am: f569f09b5a am: 75aba256b2

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/15327988

Change-Id: I6e58e79592faca842ada3ddd1c0d6fd9dcdb7e49