Fix currency symbol setting back to default #17567

[magently]

Description

Fixed currency Symbol setting back to default

Fixed Issues

1. Currency symbol cannot be changed back to default value from admin panel in Single-store mode #17567: Currency symbol cannot be changed back to default value from admin panel in Single-store mode

Manual testing scenarios

1. Set mode to Single-store in admin panel.
2. Go to currency symbols section.
3. Set custom currency symbol, then set it back to default.

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 @magently. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me {$VERSION} instance - deploy vanilla Magento instance

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[rogyar]

@magento-engcom-team give me 2.2-develop instance

[magento-engcom-team]

Hi @rogyar. Thank you for your request. I'm working on Magento 2.2-develop instance for you

[magento-engcom-team]

Hi @rogyar, here is your Magento instance.
Admin access: https://i-17966-2-2-develop.engcom.dev.magento.com/admin
Login: admin Password: 123123q
Instance will be terminated in up to 3 hours.

[rogyar]

@magento-engcom-team give me test instance

[magento-engcom-team]

Hi @rogyar. Thank you for your request. I'm working on Magento instance for you

[magento-engcom-team]

Hi @rogyar, here is your new Magento instance.
Admin access: https://pr-17966.engcom.dev.magento.com/admin
Login: admin Password: 123123q

[magento-engcom-team]

Hi @magently. Thank you for your contribution.
We will aim to release these changes as part of 2.2.8.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.