Test / Doublecheck request queue

[seeba8]

I feel like sometimes (at least in firefox), when pinboard is down / network is down / a request should fail, it silently fails and does not keep the request in the queue. Doublecheck that the request is kept in the queue in that case and only removes it in specific positive returns (whitelist, not blacklist).
At least, do that for the important requests (create bookmark, update bookmark, delete bookmark).
The rest, not too important, but fix it in one place.