Intermediate fix: Better handle network errors
requested to merge 374-bug-sync-during-difficult-network-conditions-might-accidentally-delete-items-from-a-library into master
This is an intermediate change which hopefully improves the behaviour of the app in bad network conditions. Previously, the app would continue to sync when it fails to fetch the remote folder list. However, this must not be done, because we cannot be sure about the remote state. We now stop syncing the failed directory.