Fix NullPointerException issue when user change

When info is null, we have risk to have access null point.

Change-Id: Ie6acee5c99d6297e31d46585435a735a38b19e82

src/com/android/settings/applications/RunningState.java

@@ -841,8 +841,10 @@ public class RunningState {
                             info, context.getResources());
                 }
                 String name = info != null ? info.name : null;
-                if (name == null) {
+                if (name == null && info != null) {
                     name = Integer.toString(info.id);
+                } else if (info == null) {
+                    name = context.getString(R.string.unknown);
                 }
                 userItem.mUser.mLabel = context.getResources().getString(
                         R.string.running_process_item_user_label, name);