Don't die if announce URL not found.

rtorrent state "torrent" files don't have an announce URLs but don't care if they are added.
Now we can reannounce torrents that are already running.

Stop rtorrent, reannounce both state files (and the tied torrent if exist)
Delete the <HASH>.torrent.libtorrent_resume
??????
Profit!!!
STY Use if/then instead of try/except
BF Prevent 'None' from being sent to is_valid_ip

It seems appropriate that is_valid_ip should throw an exception for
non-string inputs, so I'm putting guards prior to calling.
Merge branch 'master' into reorganization