ContentLink target is not visible if the user has not "See" permission on it. (#2211)

Author: kavics

src/ContentRepository.InMemory/InMemoryIndex.cs

@@ -197,7 +197,10 @@ public void Delete(SnTerm term)
                 deletableVersionIds.AddRange(versionIds);
             }
 
-            // delete all version ids in any depth
+            // Delete all version ids in any depth
+            // The class is not thread safe. Sometimes there is an
+            //   InvalidOperationException in the following "foreach" cycle:
+            //   "Collection was modified; enumeration operation may not execute."
             var indexesToDelete = new List<string>();
             foreach (var item in IndexData)
             {

src/Storage/NodeList.cs

@@ -563,10 +563,11 @@ internal Q GetSingleValue<Q>() where Q : Node
 
             using var systemAccount = new SystemAccount();
 
-            var user = AccessProvider.Current.GetCurrentUser();
+            var user = AccessProvider.Current.GetOriginalUser();
 
             var singleNode = RawData
-                .Select(id => Node.Load<T>(id))
+                .Select(Node.Load<T>)
+                .Where(node => node != null)
                 .OfType<Q>()
                 .FirstOrDefault(node => 
                     node.Security.HasPermission(user, PermissionType.See));