GPX plotted on map, but statistics not calculated.

Hi,

This is my first foray into both Python and GPX, so I don't really feel confident enough to figure out what's going wrong and file a bug report for it. Sorry.

I've installed the most recent version (0.4). When I open a GPX file, it's displayed perfectly on the map, but none of the statistics are displayed. I get the following error message:

Traceback (most recent call last):
  File "/usr/local/lib/python2.6/dist-packages/gpxviewer/ui.py", line 300, in onTrackAdded
    self.selectTrace(trace)
  File "/usr/local/lib/python2.6/dist-packages/gpxviewer/ui.py", line 347, in selectTrace
    distance = trace.get_distance()
  File "/usr/local/lib/python2.6/dist-packages/gpxviewer/gpx.py", line 151, in get_distance
    return self._get_cached_value("distance")
  File "/usr/local/lib/python2.6/dist-packages/gpxviewer/gpx.py", line 97, in _get_cached_value
    self._walk_points()
  File "/usr/local/lib/python2.6/dist-packages/gpxviewer/gpx.py", line 85, in _walk_points
    seconds += (pointp['time'] - segment['points'][0]['time']).seconds
TypeError: 'NoneType' object is unsubscriptable

I'd rather not upload the GPX file to Launchpad as it's got the exact location of my house in it, but I'd happily email it to you if you need it.

Thanks!

Josh