Extension opens parent folder of selected folder

I am using VS Code 1.39.2 (latest). Invoking `Open this folder as Workspace` for a top-level folder in my project does not work (no new workspace instance of VS Code launches).

I then tried to open a sub-folder of a top-level folder and this *does* open a new VS Code window, but it has opened the top-level, parent folder, not the selected sub-folder.

Example: if my open workspace is myapp with the following 3 folders and 2 files:

```
> .vscode
> server
> ui
README.md
package.json
```

then right-click | open of the `ui` folder does nothing. If, however, I expand ui to:

```
> .vscode
> server
v ui
> build
> public
> src
README.md
package.json
```

then right-click | open of the `build` subfolder opens a new Workspace rooted at `ui`, when I would expect it to be rooted at `build`.

Perhaps this is how you intended it to work, but it seems odd. If deliberate, could you explain your rationale? Thanks.

The report names no files or tests. Reproduce the behavior in VS Code 1.39.2 using the myapp folder tree described, then trace the extension command that handles opening folders and verify that selecting ui or build opens the selected folder rather than its parent.

Written by the indexing model from the issue text.