Bugfix/update address in my account

[gibkigonzo]

Short description and why it's useful

This change should prevent of creating second time default_shipping address, because right now there is error when we trying to edit shipping address.
QA:

1. initial condition - logged in user, completed data for shipping in the user's profile
2. click on the 'My account' icon
3. click the 'My shipping details' link from the side menu
4. click the 'Edit your shipping details' link
5. change the data entered in each field
6. click 'Update my shipping details' button
7. check if the changes have been saved

Which environment this relates to

Check your case. In case of any doubts please read about Release Cycle

• Test version (https://test.storefrontcloud.io) - this is a new feature or improvement for Vue Storefront. I've created branch from develop branch and want to merge it back to develop
• RC version (https://next.storefrontcloud.io) - this is a stabilisation fix for Release Candidate of Vue Storefront. I've created branch from release branch and want to merge it back to release
• Stable version (https://demo.storefrontcloud.io) - this is an important fix for current stable version. I've created branch from hotfix or master branch and want to merge it back to hotfix

Upgrade Notes and Changelog

• No upgrade steps required (100% backward compatibility and no breaking changes)
• I've updated the Upgrade notes and Changelog on how to port existing VS sites with this new feature

IMPORTANT NOTICE - Remember to update CHANGELOG.md with description of your change

Contribution and currently important rules acceptance

• I read and followed contribution rules