Merge "Add null check for mRootTaskInfo in AppPair dump" am: e39da5a9a7 am: 6b88dadc8b am: 6eb2fbbe3c am: bcaa34d13f

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1890538

Change-Id: I98c68104042fd15f7ef023d7d49bebfa7365116e