PHP 8 crash in GroupFolders trashbin when item has no extension (Undefined array key "extension")

Steps to reproduce

1. Create a Group Folder (Team folder)
2. Inside the Group Folder:
   • Create a directory or a file without extension (e.g. README)
3. Delete the directory / file
4. Open the Trashbin via web UI or via WebDAV (PROPFIND on /remote.php/dav/trashbin/*)

Expected behaviour

Group Folder trashbin should open normally and list all deleted items,
including directories and files without extensions.

Actual behaviour

The Group Folder trashbin fails to load and returns a PHP fatal error
when the trash contains directories or files without an extension.

Server configuration

Operating system: Linux
Web server: Apache
Database: PostgreSQL
PHP version: PHP 8.3
Nextcloud version: 32.0.5
Team folders version: groupfolders (shipped / custom_apps)
Updated from an older Nextcloud/ownCloud or fresh install: fresh install
Where did you install Nextcloud from: official Nextcloud package
Are you using external storage, if yes which one: local
Are you using encryption: no
Are you using an external user-backend, if yes which one: no

Client configuration

Browser: any (also reproducible via WebDAV)
Operating system: Linux

Logs

Web server error log

Nextcloud log (data/nextcloud.log)

Browser log

Additional information

• The issue only occurs when the Group Folder trash contains:
  • directories (mimetype = httpd/unix-directory), or
  • files without a file extension
• Database integrity is OK (no NULL values in name, original_location, or file_id)
• Removing folder entries from oc_group_folders_trash immediately resolves the issue
• Root cause appears to be assuming pathinfo()['extension'] always exists
• pathinfo() does not return an extension key for directories or filenames without a dot
• This leads to a PHP 8 fatal error when the value is later passed to substr()

A small defensive fix using $pathInfo['extension'] ?? '' and
$pathInfo['filename'] prevents the crash without changing behavior
for files that do have extensions.