Wrap watchdog comment in if (function_exists)

A customer has been having issues with Authorize.net IPNS. Turning off watchdog logging seems to have been the fix - probably because A.net wasn't bootstrapped.

I'm not 100% sure about that being the problem but there seems to be no downside in taking precautions. compare

/**

• @inheritDoc
  */
  public function logger($message)
  Unknown macro: { if (CRM_Core_Config}

with

if ($config->userFrameworkLogging) {
// should call $config->userSystem->logger($message) here - but I got a situation where userSystem was not an object - not sure why
if ($config->userSystem->is_drupal and function_exists('watchdog'))

{ watchdog('civicrm', '%message', array('%message' => $message), WATCHDOG_DEBUG); }

}