Handle error when converting faces with open curve loops

[vietle-bh]

Issues addressed by this PR

Closes #1462

If externalLoop is null for any reason, we'll fall back on find the loop with the max area. This is slower than checking loop winding direction, but externalLoop is null in like 1 out of 1000 faces, so the performance hit isn't bad.

Test files

@pawelbaran : Do we need a test file for this PR?

Changelog

Additional comments

[pawelbaran]

@vietle-bh I believe it would be good to have test files for such discrete bugs. It should be relatively quick to copy-paste the failing element to an empty document, then create a simple pull script that would highlight the failure - happy to help you out with the latter once you have the file with isolated element ready 👍

[pawelbaran]

@BHoMBot check required

[bhombot-ci[bot]]

@pawelbaran to confirm, the following actions are now queued: - check `code-compliance` - check `documentation-compliance` - check `project-compliance` - check `core` - check `null-handling` - check `serialisation` - check `versioning` - check `installer`

[pawelbaran]

@BHoMBot check dataset-compliance @BHoMBot check copyright-compliance @BHoMBot check ready-to-merge

[bhombot-ci[bot]]

@pawelbaran to confirm, the following actions are now queued: - check `dataset-compliance` - check `copyright-compliance` - check `ready-to-merge`