Update report.php (#1588)

This should improve #1581

If checks that parameter $_GET['id'] is passed (it's then casted to int by processor.php) but ONLY if the report.php script is called directly.
This first part of the check is necessary because report.php is included in Mage::printException()

errors/report.php

@@ -24,6 +24,8 @@
  * @license    http://opensource.org/licenses/osl-3.0.php  Open Software License (OSL 3.0)
  */
 
+if ($_SERVER['SCRIPT_FILENAME'] == __FILE__ && (!isset($_GET['id']) || strlen($_GET['id']) == 0)) die("Missing parameter: id");
+
 require_once 'processor.php';
 
 $processor = new Error_Processor();