Fix multi selection stage/discard not working for files with substrings

[brandondong]

• PR Description

I found an issue with multi selection stage/discard. Here is a minimal repro:

git init
touch a
touch aa
lazygit

Select both files using shift and hit space. Only a is staged.

• Please check if the PR fulfills these requirements

• [ ] Cheatsheets are up-to-date (run go generate ./...)
• [x] Code has been formatted (see here)
• [x] Tests have been added/updated (see here for the integration test guide)
• [ ] Text is internationalised (see here)
• [ ] Docs have been updated if necessary
• [x] You've read through your own file changes for silly mistakes etc

[jesseduffield]

@brandondong could you make an integration test for this?

[brandondong]

To try for a realistic scenario in the test, I added the workflow that led to me discovering this issue in the first place: renaming a file by adding a suffix and then trying to range select and stage both the deleted and added file.

[jesseduffield]

great work @brandondong thanks for making this