Fixed #87 Incorrect results on download check Admin

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Please simplify:
```php
function zen_has_product_attributes_downloads_status($products_id) {
  if (DOWNLOAD_ENABLED != 'true') {
    return false;
  }
  global $db;
  $query = "... snip ...";
  $result = $db->Execute($query);
  return ($result->RecordCount() > 0);
}
```
Even when just fixing bugs, it pays to take the extra time and effort to tidy things up with some incremental refactoring.
(see [Arrow Anti-Pattern](http://c2.com/cgi/wiki?ArrowAntiPattern) and [Guard Clause](http://c2.com/cgi/wiki?GuardClause))