Bugfix: Incorrect duration with track containing multiple segments

[gorgobacka]

While inspecting the gpx handling, I found a bug:
The variable stopped_time_between_seg contains only the time between the latest two segments and passes them to get_gpx_data.

This is not an issue, if the track contains only one or two segments. But if there are more, the additional calculations are incorrect.

The changed code aggregates the time between all segments now.

[SamR1]

thanks for the fix.

[gorgobacka]

Thanks for adding a test case. 👍