Fix NPE, Add null check to mActivityManager

notifyTopActivities lambda may be invoked after stop() has been called,
causing NPE

Fix: 140579356
Test: make -j

Change-Id: Ic4fb692670b77cf433717e317a9bb42eb48dbc60
1 file changed
tree: c92cc3fbb7b890d7ed94bccb13a92a6f818cb671
  1. res/
  2. src/
  3. tests/
  4. Android.mk
  5. AndroidManifest.xml