Merge "Add null check to TaskPersister file list." into lmp-dev

    private static void removeObsoleteFiles(ArraySet<Integer> persistentTaskIds, File[] files) {

        if (DEBUG) Slog.d(TAG, "removeObsoleteFile: persistentTaskIds=" + persistentTaskIds +

                " files=" + files);

        if (files == null) {

            Slog.e(TAG, "File error accessing recents directory (too many files open?).");

            return;

        }

        for (int fileNdx = 0; fileNdx < files.length; ++fileNdx) {

            File file = files[fileNdx];

            String filename = file.getName();