[Backport 2.2] MAGETWO-71697: Fix possible bug when saving address with empty street line #10582

[vovayatsyuk]

Cherry-pick of 5858ca5
Original PR: #10582

Description

The changes affect address street data preparation to guarantee that street array will be converted to the string.

Manual testing scenarios

1. Make the street address as an optional field (third-party extension is required or edit DB properties of the field)
2. Save the address without street
3. exception 'Exception' with message 'Notice: Array to string conversion on line 2903 in lib/internal/Magento/Framework/DB/Adapter/Pdo/Mysql.php will be raised.

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)