Merge "Fix NPE when re-registerNetworkCallbacks" into udc-dev am: feb922b0ce am: cfe7cf292e

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/22598874

Change-Id: I4a6c95c4009081c221519975b45ce9f888b5a711
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>