Only send JOIN message if we have channels to join

Don't send a JOIN command to upstream server when no channels are configured.

upstream.go

@@ -552,6 +552,7 @@ func (uc *upstreamConn) handleMessage(msg *irc.Message) error {
 			dc.updateSupportedCaps()
 		})
 
+		if len(uc.network.channels) > 0 {
 			// TODO: split this into multiple messages if need be
 			var names, keys []string
 			for _, ch := range uc.network.channels {
@@ -565,6 +566,7 @@ func (uc *upstreamConn) handleMessage(msg *irc.Message) error {
 					strings.Join(keys, ","),
 				},
 			})
+		}
 	case irc.RPL_MYINFO:
 		if err := parseMessageParams(msg, nil, &uc.serverName, nil, &uc.availableUserModes, nil); err != nil {
 			return err