fixing undefined variable $linkResultsFlag

[maxbeutel]

If $num_phases != 0 then $linkResultsFlag is undefined in line 403 and throws an E_NOTICE message: Notice: Undefined variable: linkResultsFlag in .../riak-php-client/riak.php on line 401

Repro code:

$client = new RiakClient();
$bucket = $client->bucket('stuff');

$mapFunc = 'function(value, keyData, arg) {
    if(value.key.indexOf("str") !== -1) return [value.key];
    return [];
}';

$result = $client->add($bucket->getName())->map($mapFunc)->reduce('Riak.reduceSort')->run();