DO NOT MERGE -- Use focused activity value when moving task back

am: da3b648b64

Change-Id: Ib706755c056ed27050375a675169f7df3f5f141a

services/core/java/com/android/server/am/ActivityStack.java

@@ -4463,7 +4463,9 @@ final class ActivityStack {
                     "moveTaskToBackAndShowHome");
         }
 
-        adjustFocusedActivityLocked(mResumedActivity, "moveTaskToBack");
+        // Using currently focused activity value from service instead of mResumedActivity,
+        // because if this happens when device is locked the mResumedActivity will be null.
+        adjustFocusedActivityLocked(mService.mFocusedActivity, "moveTaskToBack");
         mStackSupervisor.resumeFocusedStackTopActivityLocked();
         return true;
     }