Do not crash if a gpx file has an extensions tag in its route tag

[agateau]

The extensions tag is also allowed in the route tag (see https://www.topografix.com/GPX/1/1/#type_rteType).

• [x] I agree to follow the project's code of conduct.
• [ ] I added an entry to CHANGELOG.md if knowledge of this change could be valuable to users.

[urschrei]

bors try

[bors[bot]]

try

Build succeeded:

• ci result

[urschrei]

Thanks for this, @agateau. I'm happy to merge, but if you have a smaller GPX source to test with that would be great.

[agateau]

Thanks for this, @agateau. I'm happy to merge, but if you have a smaller GPX source to test with that would be great.

Sure, I just force-pushed a much shorter GPX file.

[urschrei]

bors try

[bors[bot]]

try

Build succeeded:

• ci result

[urschrei]

Bors r+

[bors[bot]]

Build succeeded:

• ci result