Users in groups excluded from sharing can initiate shares if also a member of a non-excluded group

Steps to reproduce

1. Create a "No sharing" group
2. Add a user to "No sharing" group
3. Configure to not allow "No sharing" group to initiate shares
4. Share folder with another user

Expected behaviour

The user shouldn't be able to initiate a share

Actual behaviour

The user initiate a share successfully that can be seen and modified by target user

Server configuration

Operating system:
Shared host

Web server:
Apache

Database:
MySQL 5.6.34

PHP version:
7.0.15

Nextcloud version: (see Nextcloud admin page)
11.0.0
Updated from an older Nextcloud/ownCloud or fresh install:
Fresh
Where did you install Nextcloud from:
Unarchive archive file downloaded from nextcloud site
Signing status:

No errors have been found.

List of activated apps:

If you have access to your command line run e.g.:
sudo -u www-data php occ app:list
from within your Nextcloud installation folder

The content of config/config.php:

If you have access to your command line run e.g.:
sudo -u www-data php occ config:list system
from within your Nextcloud installation folder

or 

Insert your config.php content here
(Without the database password, passwordsalt and secret)

Are you using external storage, if yes which one: no

Are you using encryption: no

Are you using an external user-backend, if yes which one: no

Client configuration

Browser: Chrome 56

Operating system: Any

Logs

Web server error log

Nextcloud log (data/nextcloud.log)

Browser log

</details>

Start by reproducing the group-sharing configuration described in the issue on a Nextcloud server, focusing on the permission check for users who belong to both excluded and non-excluded groups. Confirm that a user in an excluded group cannot initiate a share, while preserving expected sharing for permitted users; the issue names no files or tests, so locating the relevant sharing authorization code will require repository research.