[Backport] Fix infinite checkout loader on a script error

[rogyar]

Original PR: #14874

Description

Infinite checkout loader may appear when some module makes a require call but the dependency wasn't returned (Network error).

The patch changes how Magento treats isPending modules. If all dependencies are errored - treat it as loaded.

Manual testing scenarios

1. Open Magento/Checkout/view/frontend/web/js/model/quote.js
2. Insert the following code:

require([
    'jquery',
    'https://some-site/tracking/api/js'
], function ($) {}, function () {});

right after

define([
    'ko',
    'underscore'
], function (ko, _) {
    'use strict';

    // add code here

3. Navigate to checkout.
4. You can't purchase the product because the page is blocked by loader.

[magento-engcom-team]

Hi @rogyar. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.1.15 release.