Magento - Upload Image in Back Office - php

Question

I'm trying to upload an image in Sales Rules in Magento,
I follow this tutorial :
https://wiki.magento.com/display/m1wiki/How+to+create+an+image+or+video+uploader+for+the+Magento+Admin+Panel
My fields must be in native SalesRules Magento module , so I made overloading following files:
Mage_Adminhtml_Block_Promo_Quote_Edit_Form
protected function _prepareForm()
{
$form = new Varien_Data_Form(array('id' => 'edit_form', 'action' => $this->getData('action'), 'method' => 'post','enctype' => 'multipart/form-data'));
$form->setUseContainer(true);
$this->setForm($form);
return parent::_prepareForm();
}
Mage_Adminhtml_Block_Promo_Quote_Edit_Tab_Main
I add my field in _prepareForm() function
$fieldset->addField('image_promo', 'image', array(
'label' => Mage::helper('salesrule')->__('Image'),
'required' => false,
'name' => 'image_promo',
));
and in this file, I change my return:
From
return parent::_prepareForm();
To
return Mage_Adminhtml_Block_Widget_Form::_prepareForm();
And finally I'm overloading this file :
Mage_Adminhtml_Promo_QuoteController and I'm adding to saveAction() function :
if(isset($_FILES['image_promo']['name']) and (file_exists($_FILES['image_promo']['tmp_name']))) {
try {
$uploader = new Varien_File_Uploader('image_promo');
$uploader->setAllowedExtensions(array('jpg','jpeg','gif','png')); // or pdf or anything
$uploader->setAllowRenameFiles(false);
// setAllowRenameFiles(true) -> move your file in a folder the magento way
// setAllowRenameFiles(true) -> move your file directly in the $path folder
$uploader->setFilesDispersion(false);
$path = Mage::getBaseDir('media') . DS ;
$uploader->save($path, $_FILES['image_promo']['name']);
$data['image_promo'] = $_FILES['image_promo']['name'];
}catch(Exception $e) {
Mage::logException($e);
}
}else {
if(isset($data['image_promo']['delete']) && $data['image_promo']['delete'] == 1)
$data['image_main'] = '';
else
unset($data['image_promo']);
}
When I try to save without upload any files, magento work properly, but when i have an image, i not pass through my saveAction, and i'm being redirected on Dashboard ...
I'm trying to had an hidden form_key by this way in my Main.php (Second file)
$fieldset->addField('form_key', 'hidden', array(
'value' => Mage::getSingleton('core/session')->getFormKey(),
'name' => 'form_key',
));
But this doesn't change anything !
Any idea ?