File paths missing slash when app name omitted

[frankcalise]

Bug

File paths show the app name as the root directory when there is no app name provided, however the first slash is missing in the path resulting in RnDiffApppackage.json for example, rather than RnDiffApp/package.json.

It is properly slashed for directories below this.

In addition to that, there is an inconsistency where if you fill out the app name input, it's just removed altogether from the file paths.

If we're expecting the app name to not show in those title bars, then we'd just need to drop the placeholder name from the title bars (since we don't see it with a custom app name).

upgrade-helper-file-path.mp4

Steps to reproduce

Describe what you expected to happen:

1. Press Show me how to upgrade!, observe that RnDiffApp/package.json is displayed in the first title bar

2. Fill out the app name input, press Show me how to upgrade!, observe that the custom app name is displayed in the first title bar such as MyApp/package.json