fixed object keys handling

Was:
```php
<?php
var_dump(array("undefined" => 1, "undefined" => 'c', "undefined" => g(0), "hi" => "hi"));
```

Now:
```php
<?php
var_dump(array("a" => 1, "b-c" => 'c', "d-e-fh" => g(0), "hi" => "hi"));
```