<?php
class Kwc_Shop_AddToCartAbstract_FrontendForm extends Kwf_Form
{
    protected function _beforeInsert(&$row)
    {
        $row->amount = 1;
    }
}

<?php
class Kwc_Shop_AddToCartAbstract_FrontendForm extends Kwf_Form
{
    protected function _beforeInsert(&$row)
    {
        if (!$row->amount) {
            $row->amount = 1;
        }
    }
}

Fix the amount in cart
Fix the amount in cart

Subclasses can set an amount and this has to be considered
