Prevent received shares to stay on top of group folders

This was with NC 24.0.5

Steps

1. Create two users "alice" and "bob" into a group "group1"
2. Login as "alice"
3. Create a folder "share"
4. Create a subfolder "share/in_share"
5. Share "share" with "bob"
6. Login as "bob"
7. Create a folder "futuregroupfolder"
8. Move "share" to "/futuregroupfolder/share". This puts the mount point on the legit folder "exists"
9. Now we override the subdir with a group folder: as admin, create a group folder called "futuregroupfolder" and apply for the group "group1" and "admin"
10. Put a folder as admin in "futuregroupfolder/in_groupfolder"
11. Login as "bob"
12. Enter "futuregroupfolder" and observe
13. Check the oc_shar etable

=> The group folder contains both the contents "in_groupfolder" and also the received share "share" with its contents "in_share".
=> the oc_share table has a file_target pointing at "/futuregroupfolder/share"

I've seen a case where this situation was the best for an infinite loop of sorts which I couldn't reproduce yet.

In any case we should prevent such scenarios, not sure how.

When creating or renaming a group folder, detecting collisions for each users would be too expensive.
Maybe something needs to be done in the mount manager initially to detect mount point overlaps and resolve them.
Or in the sharing code verifyMountPoints where duplicate detection is happening, and check also every parent to make sure they are not point points ?

Thoughts ? @icewind1991 @CarlSchwan

Reproduce the folder and group-folder collision described in the steps, then inspect the mount manager and sharing code around verifyMountPoints. Check the resulting oc_share file_target and whether parent mount points overlap. Done means the received share is not exposed inside the group folder and the collision cannot create an infinite loop.