editing layout is broken, can't edit layout with 15 sections

Thank you for great software.

**Describe the bug**

I have monitor with Resolution 5,120 x 1,440 and I want to divide it to half then both half in to 7 sections. Tiling Shell is going crazy when I try to edit again. check screenshot.

**To Reproduce**
Steps to reproduce the behaviour:
1. create a new layout.
2. divide it to half
3. divide both section to 7 sections and save.
4. try to edit saved layout.

Target layout :
| h1c1 | h1c2 | h1c3 | h1c4 | h1c5 | h1c6 | h1c7 |
|--------|--------|--------|--------|--------|--------|--------|
| h2c1 | h2c2 | h2c3 | h2c4 | h2c5 | h2c6 | h2c7 |

**Screenshots**
edit layout have different sections with overlapping each other in weird way.

Layout export:

[tilingshell-layouts.json](https://github.com/user-attachments/files/24978246/tilingshell-layouts.json)

**Information (please complete the following):**
- Tiling Shell version: 17.3
- GNOME version: GNOME Shell 46.0
- OS: Ubuntu 24.04.3 LTS (Linux 6.11.0-29-generic)