fix(app-preview): Change how root path is determined for singular template

[ryanlanciaux]

This PR contains:

• [x] bugfix
• [ ] feature
• [ ] refactor
• [ ] documentation
• [ ] other

Are tests included?

• [ ] yes (bugfixes and features will not be merged without tests)
• [x] no

Breaking Changes?

• [ ] yes (breaking changes will not be merged unless absolutely necessary)
• [x] no

If yes, please include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers:

Description

There is an issue when there is only one template present and how the path for the sidebar is handled. This should resolve that issue but selecting the root path in a different way for singular templates.

[sysmat]

There should not be differences in path resolution from single or multiple templates

[shellscape]

@sysmat that was changed up. not to worry.