[BUG] Wrong attachment size with emails in outbox

[jiriks74]

Steps to reproduce

1. Write an email
2. Add an attachment
3. Set up Send later for this email
4. Send it
5. Go to the outbox
6. Open the email
7. See attachment size as NaN undefined

Screenshots

Expected behavior

Seeing the correct attachment size.

Actual behavior

Size is reported as NaN undefined.

Mail app version

4.0.10

Nextcloud version

30.0.4

Mailserver or service

Self-hosted SMTP server (docker-mailserver)

Operating system

Nextcloud AIO on arm64

PHP engine version

PHP 8.3

Nextcloud memory caching

'memcache.distributed' => '\OC\Memcache\Redis',

Web server

Apache (supported)

Database

PostgreSQL

Additional info

No response

[jiriks74]

Transfered from #10066 (comment)