Fix integers being cast to decimal in some particular cases

[digitalpianism]

Preconditions (*)

1. 20.0.2
2. Disable Flat Catalog.

Steps to reproduce (*)

1. Run the following script

<?php

require_once 'app/Mage.php';

Mage::app();

$collection = Mage::getModel('catalog/product')->getCollection()
    ->addAttributeToSelect('tax_class_id')
    ->addAttributeToSort('name');

// toggle this to see the weird result
$collection->addAttributeToSelect('price');

// to make the script faster and lighter
$collection->setPageSize(1);

if ($collection->getSize() > 0) {
    var_dump($collection->getFirstItem()->getData('tax_class_id'));
}

// does not help, the SQL is exactly the same
// echo (string) $collection->getSelect();

Expected result (*)

1. It should give you the tax class id as an integer, as declared for this attribute type.

Actual result (*)

1. It will give you the tax class id as a float.

Extra information

I spent a lot of time debugging this issue, you can find a detailed thread about it here: https://magento.stackexchange.com/questions/105244/magento-1-admin-product-grid-column-value-disappear-on-name-search/105421

So I already have a fix for it, will do a PR soon