child_process: buffer iterator to next before handler call

When handler that bound to forked child_process throws error,
message iterator doesn't go next and when child_process send next message, unexpected message comes.  
  
See the code below.  
```js
var assert = require('assert'), cluster = require('cluster');
var messages = ['1st', '2nd'], expected = [].concat(messages);

if(cluster.isMaster) {

  process.on('uncaughtException', function(e) {
    // avoid down
    console.log('catch exception: ', e.message);
  });

  var worker = cluster.fork();
  worker.on('online', function() {
    worker.on('message', function(m) {
      assert.equal(m, expected.shift());
      x; // <= throw error.
    });
  });

} else {

  while(messages.length)
    process.send(messages.shift());

}
```
  
We might expect the stdout result:  
```js
catch exception:  x is not defined
catch exception:  x is not defined
```
  
actual result is:  
```js
catch exception:  x is not defined
catch exception:  "1st" == "2nd"
```