Looks like you are missing a needed php tag. Should be:
<script>
( function() {
var query = document.location.search;
if ( query && query.indexOf( 'preview=true' ) !== -1 ) {
window.name = '';
}
if ( window.addEventListener ) {
window.addEventListener( 'unload', function() { window.name = ''; }, false );
}
}());
</script>