Make git_status diff works with stagged files

[zoriya]

Description

I use git_status quite often and by default, if changes are staged they are not displayed on the preview. If all changes are staged, the preview is simply blank.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Change an existing file and stage it, run :Telescope git_status and see the diff (blank before, with the file after).

Checklist:

• My code follows the style guidelines of this project (stylua)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (lua annotations)

[tjdevries]

Thanks, that's a good call! I like this change.