Fix change node overwriting msg with itself

[dceejay]

and add test
to close #3891

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

This fixes #3891 where setting change node to move a property to itself results in undefined. It should leave it unchanged
(Bit of an edge case but hey...)

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the forum/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage decreased (-0.05%) to 68.277% when pulling 3e4c45a on fix-change-self-overwrite into f060309 on master.

[Steve-Mcl]

Does this need backport?

[dceejay]

That would be ideal if there is a fix release planned.