Fix bug: Customer import deletes exiting customer entity Fields

[jalogut]

Importing a import file to update customer data, results in entity fields being removed if the columns are not present on the imported file.

That is the case for all fields defined here:

protected $customerFields = [
        CustomerInterface::GROUP_ID,
        CustomerInterface::STORE_ID,
        CustomerInterface::UPDATED_AT,
        CustomerInterface::CREATED_AT,
        CustomerInterface::CREATED_IN,
        CustomerInterface::PREFIX,
        CustomerInterface::FIRSTNAME,
        CustomerInterface::MIDDLENAME,
        CustomerInterface::LASTNAME,
        CustomerInterface::SUFFIX,
        CustomerInterface::DOB,
        'password_hash',
        CustomerInterface::TAXVAT,
        CustomerInterface::CONFIRMATION,
        CustomerInterface::GENDER,
        'rp_token',
        'rp_token_created_at',
        'failures_num',
        'first_failure',
        'lock_expires',
    ];

Importing a customer should result on adding or editing new data but it should keep previous information if the column is not present on imported file.

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)

[osrecio]

Change : to ; Please (Line 287)

[jalogut]

ups! I edited the commit. Thanks for noticing.

[dmanners]

Could you maybe a docblock to this method with a short explanation of the bug this method fixes. Is there actually a github issue for this fix cause you could add a link to that here.