Side panel doesn't show the pre-selected chapter as marked

[jacobwod]

DocumentHandler's side panel should start with the selected chapter pre-marked in the side panel:

Correct behaviour in bae432a

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Somewhere along the way, it seems that we lost this functionality. The same configuration files lead to this result on recent codebase:

Marker is lacking in newer releases, e.g. f172c2f

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Quite a lot has happened in the code between these two points, including the upgraded MUI version. Probably we just missed some detail.

[jacobwod]

So this is worrying: two pretty important props (document and model) are null:

[Hallbergs]

Ugh. Probably some timing issue related to the react 18 upgrade. Let's look into it.