Checkout - Fix "Cannot read property 'code' on undefined" issue

[ihor-sviziev]

Description

After upgrading from 2.2.5 to 2.2.6 with module One Step Checkout module we started getting js error "Cannot read property 'code' of undefined".
Reason - this module removes all checkout "steps", but in Magento code there is no check that we have at least one step.

Fixed Issues (if relevant)

1. Checkout - Cannot read property 'code' of undefined #18164: Checkout - Cannot read property 'code' of undefined
2. Cannot read property 'code' of undefined mageplaza/m2-one-step-checkout-releases#3: Cannot read property 'code' of undefined

Manual testing scenarios

1. Add to checkout page js component that will require 'Magento_Checkout/js/model/step-navigator'
2. Add in it stepNavigator.steps.removeAll(); to remove all steps
3. Go to checkout, look in console

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @sidolov, thank you for the review.
ENGCOM-3153 has been created to process this Pull Request

[magento-engcom-team]

Hi @ihor-sviziev. Thank you for your contribution.
We will aim to release these changes as part of 2.3.1.
Please check the release notes for final confirmation.