Reproduction steps

1. Use this snippet:

foo bar baz
foo
foo bar

2. Put the cursor at the end of line 1
3. editor::AddSelectionBelow twice

Current vs. Expected behavior

There should be a cursor at the end of each line.

Instead, once a cursor is added on the shorter line 2, the original cursor offset is forgotten, so you get this:

I think this originally worked in #40190, but I suspect it broke in #45594.

cc @dinocosta

Zed version and system specs

Zed: v0.219.4+stable.119.5595f7ce23d51a58eb66dd025a487bbd6c75dad1 (Zed)
OS: macOS 15.7.3
Memory: 16 GiB
Architecture: x86_64