git: fix discard all for unstaged files

[vince-fugnitto]

What it does

Fixes: #11675.

The pull-request fixes discard all when there are unstaged files.
The previous logic would not filter the newly created files, and throw dugite errors.

How to test

1. start the application with a workspace under version control
2. perform changes in the workspace including creating new files (unstaged)
3. perform discard all from the scm-view
4. confirm that the changes are discarded, and no errors are thrown

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

Signed-off-by: vince-fugnitto [email protected]

[msujew]

I can confirm that the issue appears on master and is addressed by your changes 👍