Bug - Queue filter in AgentTicketStatusView not working correctly

[ZTrotter]

Environment

• Server OS: Oracle Linux
• Browser: Chrome, Edge
• Znuny version: 7.0.16

Expected behavior

After clicking on the queue filter in AgentTicketStatusView, the user should be displayed the list of the queues currently available to filter by, based on the tickets in the list.

Actual behavior

If a sub queue is present in the list, instead of a drop-down with the queues, the dropdown gets stuck on "Loading ..."
This behaviour also appears in AgentTicketEscalationView.

How to reproduce

Steps to reproduce the behavior:

1. Go to AdminQueue and create two queues and a subqueue for each
2. Create two new tickets, one in each subqueue
3. Go to AgentTIcketStatusView
4. Click on the filter icon next to Queues to bring up the filter options
5. Click on the arrow to open the drop down menu
6. See that event sticks on "Loading ..."

Additional information

After extensive testing, it is stell not clear to us the source of the issue. We presume the bug to be in this function Core.UI.TreeSelection.ShowTreeSelection(). The return value of this function looks a little odd:

The queue with the id "9" has a child inside of it having the id "10".
The queue with the id "5" has no children inside of it (underlined in red). However, when looking into the queue with the id "6", one can see that it is a "ChildOf" the queue "5".

Screenshots

Stuck on "Loading ..."

[rkaldung]

Internal issue 880