Fix skipping a file when staging last file in a directory

[Tillerino]

This Pull Request partly addresses #2748.

The "error" result from the binary search was not taken into account after an update to the status tree, which lead to files being skipped when the last file in a directory was staged.

Before:

Screencast_20251029_204232.webm

(skips zzz)

After:

Screencast_20251029_204327.webm

I followed the checklist:

• [X] I added unittests
• [X] I ran make check without errors
• [X] I tested the overall application
• [X] I added an appropriate item to the changelog

[extrawurst]

@Tillerino could you fix the conflicts?

[extrawurst]

@Tillerino would love to see this land, are you committed to push it over the finish line?

[Tillerino]

I rebased and incorporated the requested changes. Ready to go.