можно как то так
$data['categories'] = array();
$results = $this->model_catalog_category->getCategories($category_id);
// тута
if(!$results){
$c_id = array_shift($parts);
$results = $this->model_catalog_category->getCategories($c_id);
}
foreach ($results as $result) {
$filter_data = array(
'filter_category_id' => $result['category_id'],
'filter_sub_category' => true
);
$data['categories'][] = array(
'name' => $result['name'] . ($this->config->get('config_product_count') ? ' (' . $this->model_catalog_product->getTotalProducts($filter_data) . ')' : ''),
'href' => $this->url->link('product/category', 'path=' . $this->request->get['path'] . '_' . $result['category_id'] . $url)
);
}