Since the attachment fetching/parsing is already asynchronous, possibly delaying the dispatching of an "attachmentsloaded" event should thus not be a problem in general.
Note that in some cases, i.e. PDF documents with no "regular" attachments and only FileAttachment annotations, we'll thus no longer dispatch an "attachmentsloaded" event when `attachmentsCount === 0` and instead wait for the FileAttachment parsing to finish. (The use of a timeout still guarantees that an "attachmentsloaded" event is *eventually* dispatched though.)
This patch *considerably* simplifies the "attachmentsloaded" event handler, in `PDFSidebar`, since the details are now abstracted away from the consumer.
Finally, add a check in `_appendAttachment` to ensure (indirectly) that the FileAttachment annotation is actually relevant for the active document.
0b65d4cacd