Fix memory safety problem with Array.from_cpointer

[ergl]

Fixes #3668. String already checked for a potential null pointer before constructing, so it was safe. Also added a test case to check this.

[ponylang-main]

Hi @ergl,

The changelog - fixed label was added to this pull request; all PRs with a changelog label need to have release notes included as part of the PR. If you haven't added release notes already, please do.

Release notes are added by creating a uniquely named file in the .release-notes directory. We suggest you call the file 3675.md to match the number of this pull request.

The basic format of the release notes (using markdown) should be:

## Title

End user description of changes, why it's important,
problems it solves etc.

If a breaking change, make sure to include 1 or more
examples what code would look like prior to this change
and how to update it to work after this change.

Thanks.

[ergl]

Not sure what's up with that failed check, it's erroring with Segmentation fault (core dumped), but didn't fail every time. Is this something that has happened before? (also, didn't think my last commit would trigger ci, maybe [skip ci] only applies outside PRs?)

[SeanTAllen]

There's a bug I'm working on that causes periodic segfaults. That's probably what the issue is.

[SeanTAllen]

Excellent title.

[ergl]

Thanks!

[jasoncarr0]

LGTM. Thanks for all the fixes

[ergl]

@SeanTAllen This should be ready to merge, I believe. Do you want to wait until the periodic segfault issue is resolved?

[SeanTAllen]

@ergl I'm going to wait to merge for a bit until hopefully the segfault is resolved. The next release is in 3 weeks (if not sooner). It should definitely be merged by then.