cluster: fix cluster rr distribute error when accept fails.

lib/internal/cluster/round_robin_handle.js

@@ -98,6 +98,10 @@ RoundRobinHandle.prototype.remove = function(worker) {
 };
 
 RoundRobinHandle.prototype.distribute = function(err, handle) {
+  // If `accept` fails just skip it (handle is undefined)
+  if (err) {
+    return;
+  }
   append(this.handles, handle);
   // eslint-disable-next-line node-core/no-array-destructuring
   const [ workerEntry ] = this.free; // this.free is a SafeMap

test/parallel/test-cluster-accept-fail.js

@@ -0,0 +1,30 @@
+// Flags: --expose-internals
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
+const cluster = require('cluster');
+const rr = require('internal/cluster/round_robin_handle');
+
+if (cluster.isPrimary) {
+  const distribute = rr.prototype.distribute;
+  rr.prototype.distribute = function(err, handle) {
+    assert.strictEqual(err, 0);
+    handle.close();
+    distribute.call(this, -1, undefined);
+  };
+  cluster.schedulingPolicy = cluster.SCHED_RR;
+  cluster.fork();
+} else {
+  const server = net.createServer(common.mustNotCall());
+  server.listen(0, common.mustCall(() => {
+
+    const socket = net.connect(server.address().port);
+
+    socket.on('close', common.mustCall(() => {
+      server.close(common.mustCall(() => {
+        process.disconnect();
+      }));
+    }));
+  }));
+}