Jonas Jenwald 05b0798824 Check that the correct pdfDocument is still active, before rendering the outline/attachments/layers
*This patch fixes some technical debt in the viewer.*

Given that most API methods are (purposely) asynchronous, there's always a risk that the viewer could have been `close`d before the requested data arrives.
Lately we've started to check this case before using the data, to prevent errors and/or inconsistent state, however the outline/attachments/layers fetching and rendering is old enough that it pre-dates those checks.
2021-04-10 13:12:40 +02:00
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