Webform attachments not sending

Problem/Motivation

On 8.x-2.2, the webform attachments on S3FS were sending correctly.

After upgrading to 8.x-2.3, the webform attachments stopped attaching.

Steps to reproduce

1. Create a test webform with a File element.
2. Set up email handler with 'Include files as attachments' enabled.
3. Use Sendgrid_integration
4. Submit Webform with file attachment.

Email does not contain any attachments.

Proposed resolution

I believe the issue is because of

        if (isset($attachment['filepath'])) 

in SendGridMail.php

For Webform attachments, the filepath has the private path, but the actual attachment is in $attachment['filecontent'].

In previous version the check was isset($attachment['uri']), which was empty, and would go to the else condition to process the attachment correctly.