orphan articles (not associated with any journal) cause the /manager page to throw an error

[hardyoyo]

Describe the bug
If one has a small collection of orphan articles (not associated with any journal), the /manager page ceases to function. Specifically, it throws this error:

https://gist.github.com/hardyoyo/6a0a765ef55ed0b6cc5c28ee9c68f15a

The manager page should be made more resilient, so it can tolerate the presence of orphan articles.

Janeway version
v1.5.0-RC-4

To Reproduce
Steps to reproduce the behavior:

1. Have a journal with some test articles
2. using an SQL tool, remove the journal_id for an article
3. Attempt to visit the /manager url for your site
4. See error

Expected behavior
The manager page should work, despite the presence of orphaned articles. It could be nice to provide a count of orphaned articles and a warning that they exist. But that's not necessary to address this ticket. The page should just work.

Screenshots
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Front-end Issues

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Smartphone (please complete the following information):
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Additional context
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