cluster: avoid race enabling debugger in worker

Previously if a worker's state machine had already transitioned into the
'listening' state when it received the message enabling the debugger,
the worker would never enable its debugger.

Change the logic to allow the 'listening' as a valid state for enabling
the debugger.

Fixes: nodejs#6440
Original-PR-URL: nodejs#9037
Signed-off-by: Julien Gilli <[email protected]>

Fixes: nodejs/node#340
PR-URL: nodejs/node#501
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: Bert Belder <[email protected]>
Reviewed-By: Rod Vagg <[email protected]>

Author: tjfontaine

lib/cluster.js

@@ -266,7 +266,7 @@ function masterInit() {
       var key;
       for (key in cluster.workers) {
         var worker = cluster.workers[key];
-        if (worker.state === 'online') {
+        if (worker.state === 'online' || worker.state === 'listening') {
           process._debugProcess(worker.process.pid);
         } else {
           worker.once('online', function() {