SystemUI: Fix possible NPE

isTaskAboveTask() results in an NPE if the caller is null.
Wrap with null checks on lauchTargetTask and
launchTargetTask.group to prevent this

Change-Id: I372ea7744c67ddd11d9731e6bee1858d4dd3318c
Reference: BugDumps 20161021-27 L#77
1 file changed