Remove margin-right of mailbox counter if it has sub mailboxes

[ChristophWurst]

Steps to reproduce

1. Configure an account
2. Have or create a two level mailbox hierarchy
3. Have or create unread messages in the first level mailbox
4. Look at the sidebar

Expected behavior

Efficient use of space

Actual behavior

🖼️	🔍	🔎

Mail app version

3.5

Mailserver or service

No response

Operating system

No response

PHP engine version

None

Web server

None

Database

None

Additional info

No response