Protect against JSON.parse potentially failing

What does this MR do and why?

For #536089 (closed)

Wraps a JSON.parse call in a try/catch to prevent against a null-ish value causing a fatal error.

See the commit message for more, but this shouldn't be possible during normal operation of the app, we're just adding a safeguard.

References

• This closes a followup issue, which came from: !187457 (merged)

Screenshots or screen recordings

No visual changes.

How to set up and validate locally

It's not really possible to test this using the UI, as it can't really happen under normal circumstances.

One way to do it would be to:

• open the reviewer dropdown,
• then - ensuring the dropdown doesn't close - modify sessionStorage so that the key points to invalid JSON data (like "#"),
• and then un-freeze the UI and select a reviewer.

For this to work, you only need to prevent the dropdown from closing, since having to re-open it would overwrite your injected data.

MR acceptance checklist

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