fix: mask out rule permissions before merging permissions

[icewind1991]

To test:

• Create group1 and group2
• Create user1 and add it to group1 and group2
• Create a groupfolder with access to group1 and group2 and acl enabled
• On the groupfolder, set all permissions to allow for group1, and all except read to deny for group2
• Create a subfolder folder
• On the subfolder, set all to deny for group2.
• occ groupfolders:permissions 1 should list the following permissions

+--------+---------------+-----------------------------------------+
| Path   | User/Group    | Permissions                             |
+--------+---------------+-----------------------------------------+
| /      | group: group2 | -write, -create, -delete, -share        |
|        | group: group1 | +read, +write, +create, +delete, +share |
| folder | group: group2 | -read, -write, -create, -delete, -share |
+--------+---------------+-----------------------------------------+

User1 has no access to the subfolder, as it is denied through group2

• On folder, set all share permissions to deny and the rest to inherit
• occ groupfolders:permissions 1 should list the following permissions

+--------+---------------+-----------------------------------------+
| Path   | User/Group    | Permissions                             |
+--------+---------------+-----------------------------------------+
| /      | group: group2 | -write, -create, -delete, -share        |
|        | group: group1 | +read, +write, +create, +delete, +share |
| folder | group: group1 | -share                                  |
|        | group: group2 | -read, -write, -create, -delete, -share |
+--------+---------------+-----------------------------------------+

On master: user1 now suddenly has access to the folder, even though there should be no new allow permissions for them.

With this PR his permissions are still denied.