Description:
------------
Error when using pcntl_wait inside handle function

Test script:
---------------
<?php
ini_set('display_errors', 1);
error_reporting(E_ALL);

$client = new GearmanClient;
$client->addServer();
$client->addTaskBackground('handle', 'test');
$client->runTasks();
######################################################
<?php
ini_set('display_errors', 1);
error_reporting(E_ALL);

function doJob($i){
	if($pid = pcntl_fork()){
		return true;
	}
	if(-1 === $pid){
		throw Exception('Unable to fork process');
	}
	sleep($i);
	file_put_contents('test.log', 'Forked child' . PHP_EOL, FILE_APPEND);
	exit;
}

$worker = new GearmanWorker;
$worker->addServer();
$worker->addFunction('handle', function(GearmanJob $job){
	for($i = 0; $i < 10; ++$i){
		doJob($i, $job->workload());
	}
	$status = null;
	while(0 < ($pid = pcntl_wait($status))){
		file_put_contents('test.log', 'child closed: ' . $pid . '(' . var_export($status) . ')' . PHP_EOL, FILE_APPEND);
	}
	$job->sendComplete('ok');
});
$worker->setTimeout(5000000);
if(!$worker->work()){
	echo 'failed';
}
echo 'done';


Expected result:
----------------
Job complete normaly

Actual result:
--------------
Job fails and returns to queue