private void OnPhaseChanged(IntPtr converter)
        {
            var tmp = NativeCalls.wkhtmltopdf_phase_description(converter, _currentPhase);
            var str = Marshal.PtrToStringAnsi(tmp);

            try
            {
                PhaseChanged(this, new EventArgs <int, string>(++_currentPhase, str));
            }
            catch (Exception ex)
            {
                _Log.Error("PhaseChanged event handler failed.", ex);
            }
        }