Monitor names/indices messed up (again)

**Describe the bug**
Hey! I've already reported the exact same bug but with one external monitor: #92
Sooo now I've connected two — and everything has broken again.

The layout of the builtin monitor changes when I edit the 3rd row in the list, not 1st:

**To Reproduce**
Honestly no idea.

**Screenshots**

**Information (please complete the following):**
- Tiling Shell version: 13.0
- GNOME version: 47.0

**Additional context**
Journal logs:
```
Sep 17 19:12:27 efog-laptop gnome-shell[264017]: [tilingshell] [extension] extension is enabled
Sep 17 19:12:28 efog-laptop gnome-shell[264017]: [tilingshell] [DefaultMenu] [{"name":"Samsung Electric Company 27\"","x":1648,"y":0,"width":2560,"height":1440},{"name":"Samsung Electric Company 27\"","x":4208,"y":0,"width":2560,"height":1440},{"name":"Built-in display","x":0,"y":0,"width":1648,"height":1030}]
Sep 17 19:21:59 efog-laptop gnome-shell[264017]: [tilingshell] [extension] building a tiling manager for each monitor
Sep 17 19:21:59 efog-laptop gnome-shell[264017]: [tilingshell] [TilingManager 0] Work area for monitor 0: 2560 0 2560x1440
Sep 17 19:21:59 efog-laptop gnome-shell[264017]: [tilingshell] [TilingManager 1] Work area for monitor 1: 0 0 2560x1440
Sep 17 19:21:59 efog-laptop gnome-shell[264017]: [tilingshell] [TilingManager 2] Work area for monitor 2: 1679 1472 1648x998