Resolves#4248
## Description:
Fix river not connected in Balkans map along the map border. The map
generator accidentally deleted some columns of pixels along the map
limits, and it disconnected a river.
<img width="588" height="482" alt="image"
src="https://github.com/user-attachments/assets/2c78b6bd-d669-4aef-bc1d-c69d4aeed162"
/>
Updated version
<img width="290" height="311" alt="image"
src="https://github.com/user-attachments/assets/f315bdfc-bcca-400d-95a7-876c14e47400"
/>
## Please complete the following:
- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
## Please put your Discord username so you can be contacted if a bug or
regression is found:
tri.star1011
RickD004
32011d2ed2