fix #866: SOCKS5 nil ptr TLSConfig in selector

Move SetDefaultTLSConfig before register(cfg) in loader.go so
ParseService can access it when building handlers. Also add a
defensive nil check in socks5 serverSelector.Select() for
MethodTLS to prevent future ordering regressions.

Root cause: in selector.go, Select() tried to read ClientHello
via TLSConfig.GetConfigForClient but s.TLSConfig was nil because
register(cfg) -> ParseService -> handler Init ran before
SetDefaultTLSConfig was called from loader.go.

config/loader/loader.go

@@ -78,12 +78,12 @@ func (l *loader) Load(cfg *config.Config) error {
 	}
 	logger.SetDefault(logger_parser.ParseLogger(&config.LoggerConfig{Log: logCfg}))
 
+	parsing.SetDefaultTLSConfig(tlsCfg)
+
 	if err := register(cfg); err != nil {
 		return err
 	}
 
-	parsing.SetDefaultTLSConfig(tlsCfg)
-
 	return nil
 }