Since f21e1b2d32, a full local file scan no longer runs periodically and
on every manual sync, so locally missed attachments stayed marked for
upload and were skipped as unavailable instead of being downloaded.
"Reset File Sync History" marked every attachment for upload, including
files that had never been downloaded, so the forced download check added
in 404fc41b88 found nothing to download.
Missing files are now marked for download when the upload queue is
filled, and in at-sync-time mode they're downloaded in the same sync.
The reset marks them for download directly, and downloads are no longer
skipped just because there were no remote storage changes.
https://forums.zotero.org/discussion/133414/
(cherry picked from commit a1ea7037c2)
1ee75da2f7
