fix exception that appears in logs if session ends before last call status update

lib/utils/ws-requestor.js

@@ -138,7 +138,7 @@ class WsRequestor extends BaseRequestor {
 
     /* simple notifications */
     if (['call:status', 'verb:status', 'jambonz:error'].includes(type) || reconnectingWithoutAck) {
-      this.ws.send(JSON.stringify(obj), () => {
+      this.ws?.send(JSON.stringify(obj), () => {
         this.logger.debug({obj}, `WsRequestor:request websocket: sent (${url})`);
         sendQueuedMsgs();
       });