[BUG]: Floodfill spills outside of selected area

Bug Description

https://github.com/user-attachments/assets/e964f6bf-bc43-4bbb-99c7-4ed70fe8c166

it's not 100% consistent but happens more often than not. Creating a new canvas and redoing everything from scratch does seem to consistently reproduce this. In video the version is 2.1.1.7 but I can also reproduce this on latest master

Steps how to trigger the issue

1. Make a 4000x3000 canvas
2. Draw random lines like I did in the video
3. Select a big area one it
4. Floodfill the area
5. Wait for floodfill to finish
6. See how it spilled along the borders of the chunks that had random lines previously drawn in them chunks

How did you download the software?

Built from source

Version Channel

Stable

Version Number

2.1.2.1 commit 5fbc1562bed1e6 (rn it's latest master)

Operating System

Windows

OS Version

Win 11

Additional Context

No response

Code of Conduct

• I agree to follow this project's Code of Conduct