adding a torrent with POST /torrents fails
with http status 400 and the response text
{"error_kind":"internal_error","human_readable":"error adding torrent: File exists (os error 17)","status":400,"status_text":"400 Bad Request"}
... when these cache files already exist
~/.cache/rqbit/{btih}.bitv
~/.cache/rqbit/{btih}.torrent
workaround: remove the cache files and retry adding the torrent