/**
 * call-seq:
 *  last_track_num() -> int or nil
 * 
 * Return the number of the last track on this disc.
 * 
 * Returns +nil+ if no ID was yet read.
 */
static VALUE mb_discid_last_track_num(VALUE self)
{
        if (rb_iv_get(self, "@read") == Qfalse)
                return Qnil;
        else
        {
                DiscId *disc;
                Data_Get_Struct(self, DiscId, disc);
                
                return INT2FIX(discid_get_last_track_num(disc));
        }
}