Fix Swarm Save and load with units

[arijitlaik]

fixes #648

PR Checklist

• [x] I have read the CONTRIBUTING.rst document.
• [x] I have updated the docstrings accordingly.
• [ ] I have updated CHANGES.md.
• [ ] I have added tests which give complete coverage for my changes.
• [ ] I have provided a usage example for my changes.
• [ ] All new and existing tests pass.

[julesghub]

Sorry for the wait on this PR @arijitlaik. I committed a similar fix a while back and forgot to inform you, see 67cbf71c. So I'll close this PR down.

I'm in the process of a 2.14.2 release with the fix in it. Thanks again for raising the issue.