failed to load track without elevation

[philippe-queinnec]

If a track has no elevation ( tag), or if the first point of a track has no elevation, loading fails.
The culprit is line 488 in _parse_segment. The line
ll.meta.ele = last.meta.ele;
should be
if (last != null) { ll.meta.ele = last.meta.ele; }

[pimschaaf]

Without this change I get the following error message:
Uncaught TypeError: Cannot read properties of null (reading 'meta') at i._parse_segment (gpx.js:488)
when elevation data is missing.

[mpetazzoni]

Thanks!