Describe the bug
This is a bug report from @jott3077.

If we create a new contour level on top of the levels generated with the level generator and delete it, the level is not deleted. Instead, the adjacent level is deleted.

To Reproduce
Steps to reproduce the behavior:

1. load an image and launch the contour configuration dialog
2. use the level generator to compute five levels
3. add a new level by clicking the histogram
4. try to use the x button to delete the just created level
5. we will see the adjacent level is deleted, not the one we created.

Expected behavior
on step 4, we should see the newly created level being deleted. The x button per level should be functional as intended.

Platform info (please complete the following information):

• OS [e.g. macOS Monterey]: macOS Monterey
• Browser [e.g. chrome, safari, electron app]: electron app
• Browser version [e.g. 22]: v3-stable electron app
• Backend branch [e.g. dev, v3b2 release]: v3-stable
• Frontend branch [e.g. dev, v3b2 release]: v3-stable