fix: init standalone-app if no templates are selected

[MichaelGoberling]

Description

If the user does not select any templates, initialize a standalone application.

Related Issue

closes #591

Motivation and Context

This fixes a workflow that results in an un-deployable App Builder application.

How Has This Been Tested?

• Locally linked app plugin
• Locally ran npm run test

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.