Check if values are set in Zend\Db\Sql\Insert.php for prepared statement

Check if values are set in Send\Db\Sql\Insert 

Fixes code for..

```php
$dbConnection->beginTransaction();
$columns = array('title', 'description');
$values = array(
 'Test',
 'Test'
);
$insert = $sql->insert()->columns($columns);
$stmt = $sql->prepareStatementForSqlObject($insert);            
$stmt->execute($values);
``

Issue here: https://github.com/zendframework/zf2/issues/3847