WebSocketDaemon attempted spawn even when ws_doc_root is null

If ws_doc_root is null (default in config.default.json), server.py still attempts to spawn WebSocketDaemons, which then fail due to lack of config.

I'm pretty new to wpt so not sure if desired behavior in this case is to

a) Require that ws_doc_root be set b) If ws_doc_root is not set, skip spawning WebSocketDaemon c) Make WebSocketDaemon handle null and default config better

For now, I assuming b) but defer to experts in terms of how this should be handled.