For some reason, we have files in the processing folder that are already present before moving. Skip those files instead of crashing with:
webdav3.exceptions.ResponseErrorCode: Request to https://nc.torproject.net/remote.php/dav/files/dangerzone-bot/CVS/dangerzone-processing/2/ failed with code 412 and message: b'<?xml version="1.0" encoding="utf-8"?>\n<d:error xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns">\n <s:exception>Sabre\\DAV\\Exception\\PreconditionFailed</s:exception>\n <s:message>The destination node already exists, and the overwrite header is set to false</s:message>\n <s:header>Overwrite</s:header>\n</d:error>\n'