Do not trigger error if response is empty

This happens from time to time with some
Selenium2 servers. And checking for empty
responses is Selenium2 job, not CURL anyway.

Author: everzet

lib/WebDriver/Service/CurlService.php

@@ -83,7 +83,7 @@ public function execute($requestMethod, $url, $parameters = null, $extraOptions
         $rawResults = trim(curl_exec($curl));
         $info = curl_getinfo($curl);
 
-        if ($error = curl_error($curl)) {
+        if (URLE_GOT_NOTHING !== curl_errno($curl) && $error = curl_error($curl)) {
             $message = sprintf(
                 'Curl error thrown for http %s to %s%s',
                 $requestMethod,