Fix restoration of a tree snapshot

Steps to reproduce

1. copy to nxserver/bundles the 3 jars attached to this ticket: the default nuxeo-tree-snapshot-7.10.jar and some addons to provide a button to create snapshots
2. Inside Default domain > Workspaces, create a Workspace whose name is "workspace", and inside "workspace", create a new Workspace whose name is "Work"
3. navigate to Default domain > Workspaces > workspace
4. click on "CreateTreeSnapshot" button
5. a snapshot is created and you can see in the content view the version is incremented to 1.0
6. create a wokspace whose name is TestFolder1 under Default domain > Workspaces > workspace > Work
7. navigate to Default domain > Workspaces > workspace
8. click on "CreateTreeSnapshot" button
9. a snapshot is created and you can see in the content view the version is incremented to 2.0
10. create a wokspace whose name is TestFolder2 under Default domain > Workspaces > workspace > Work
11. navigate to Default domain > Workspaces > workspace
12. click on "CreateTreeSnapshot" button
13. a snapshot is created and you can see in the content view the version is incremented to 3.0
14. Go to History tab and then to Archived versions sub-tab
15. Restore Version 2.0
16. you can see in the content view the version for the Work document 2.0 as expected
17. create a wokspace whose name is TestFolder3 under Default domain > Workspaces > workspace > Work
18. navigate to Default domain > Workspaces > workspace
19. click on "CreateTreeSnapshot" button
20. a snapshot is created and you can see in the content view the version is incremented to 4.0
21. Go to History tab and then to Archived versions sub-tab
22. Restore Version 3.0

=> it produces an error, with DocumentNotFoundException

8790075d-b79b-40dd-bca9-1f418a9c53af

               javax.servlet.ServletException: On requestURL: http://nereid2:8080/nuxeo/view_documents.faces
	at org.nuxeo.ecm.platform.ui.web.rest.FancyURLFilter.doFilter(FancyURLFilter.java:134)
	
Caused by: javax.servlet.ServletException: org.nuxeo.ecm.core.api.DocumentNotFoundException: 8790075d-b79b-40dd-bca9-1f418a9c53af

Caused by: javax.faces.el.EvaluationException: org.nuxeo.ecm.core.api.DocumentNotFoundException: 8790075d-b79b-40dd-bca9-1f418a9c53af

	... 62 more
Caused by: org.nuxeo.ecm.core.api.DocumentNotFoundException: 8790075d-b79b-40dd-bca9-1f418a9c53af
	at org.nuxeo.ecm.core.storage.sql.coremodel.SQLSession.getDocumentByUUID(SQLSession.java:171)
	at org.nuxeo.ecm.core.api.AbstractSession.resolveReference(AbstractSession.java:326)
	at org.nuxeo.ecm.core.api.AbstractSession.getDocuments(AbstractSession.java:949)
	at org.nuxeo.snapshot.SnapshotableAdapter.getChildren(SnapshotableAdapter.java:175)
	at org.nuxeo.snapshot.SnapshotableAdapter.restore(SnapshotableAdapter.java:285)
	at org.nuxeo.snapshot.SnapshotableAdapter.restore(SnapshotableAdapter.java:325)
	at org.nuxeo.snapshot.SnapshotableAdapter.restore(SnapshotableAdapter.java:340)
	at org.nuxeo.snapshot.bean.VFolderActionBean.restoreToVersion(VFolderActionBean.java:40)