fix php 7.2 error : Countable interface not implemented

[gmachure]

Description (*)

We created a custom module with ui component form with a file upload field. While the upload, the method _setUploadFileId from vendor/magento/framework/File/Uploader.php generate a warning because Countable interface is not implement for a string (PHP version : 7.2.12).
$file[0] is a string and not an array. So count($file[0]) generate an error.

Fixed Issues (if relevant)

1. Magento 2 : fix php 7.2 error : Countable interface not implemented #19247: fix php 7.2 error : Countable interface not implemented

Manual testing scenarios (*)

1. Upload image in ui component form in a custom module
2. Test :
   -Create custom module
   -Add a file uploader in ui component form.
   -Upload an image.
   -PHP version : 7.2.12

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 @gmachure. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
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[gmachure]

@magento-engcom-team give me test instance

[magento-engcom-team]

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

[magento-engcom-team]

Hi @gmachure, here is your new Magento instance.
Admin access: http://34.228.235.121/pr-19249//admin
Login: admin Password: 123123q

[magento-engcom-team]

Hi @orlangur, thank you for the review.
ENGCOM-3483 has been created to process this Pull Request

[magento-engcom-team]

@gmachure thank you for contributing. Please accept Community Contributors team invitation here to gain extended permissions for this repository.

[magento-engcom-team]

Hi @gmachure. 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.