Slot order is incorrect after changing the draw order in animate mode

[misaki-eymard]

Description:
If the drawing order is changed while multiple slots are selected in animate mode, the slot order is incorrect. For example, suppose the slots are lined up as shown in the following image:

Select slot1 and slot2 and move over slot3.

After the move, the order of slot1 and slot2 will be swapped, as shown below:

Expected behavior:
The order does not change among the selected slots. In the example above, the order of slot2 up and slot1 down should be maintained after the move.

Steps to reproduce:

1. Open the spineboy-pro.spine via the Examples section on the welcome screen.
2. Switch to the animate mode.
3. Select the muzzle-ring and the muzzle-ring2 slots under the Draw order section in the tree view.
4. Drag and drop them to over the muzzle-ring4 slot. Then, you can see the muzzle-ring slot is on top and the muzzle-ring2 slot is below it.

The version of Spine in which this bug was found:
Spine 4.2.19

This issue was reported on the following thread:
https://esotericsoftware.com/forum/d/26117-modify-layer-order-default-order-error

[NathanSweet]

I don't remember which change fixed this, but I don't see it happening in 4.2.21.