protected void onDemandLoadAndSetupPreviousTrailer() {
//System.out.println("PTrailer.onDemandLoadAndSetupPreviousTrailer() : " + this);
//try { throw new RuntimeException(); } catch(Exception e) { e.printStackTrace(); }
        long position = getPrev();
        if (position > 0L) {
            PTrailer prevTrailer = library.getTrailerByFilePosition(position);
            if (prevTrailer != null)
                addPreviousTrailer(prevTrailer);
        }
    }