Sublayers not displayed in Bookmarks plugin

[linusfj]

Describe the bug
When activating a bookmark that contains group layers from WMS services, the sublayers within the group layers are not properly displayed on the map. The group layer itself is activated, but its sublayers are not visible.

To Reproduce
Steps to reproduce the behavior:

1. Add a WMS group layer that contains sublayers to the map.
2. Create and save a bookmark that includes the group layer.
3. Activate the bookmark.
4. Notice that while the group layer appears as activated, its sublayers are not visible on the map.

Expected behavior
When a bookmark containing a WMS group layer is activated, the sublayers should also be displayed correctly on the map.