[bugfix] - viewer.py navmesh recompute skip for "none" scene

[aclegg3]

Motivation and Context

When choosing to skip navmesh recompute for none scene, need to handle cases where the "NONE" scene is not all upper case.

How Has This Been Tested

locally

Types of changes

• Docs change / refactoring / dependency upgrade
• 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

• 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 completed my CLA (see CONTRIBUTING)
• I have added tests to cover my changes.
• All new and existing tests passed.