Navigation-related stuff references Nav. groups when Nav. settings are missing

Release Type: Official Release

Version: 4.1.0.1459

Platform(s): Windows (in-editor)

Describe the bug
When a user adds Navigation component and/or NavigationMesh asset he is able to select the default New group navigation group that is present in the default project navigation settings, and because there are no navigation settings added to GameSettings by default it results in an error:

When you press on a navgroup when nav settings are not added nothing is changed and those errors appear:

To Reproduce
Steps to reproduce the behavior:

1. Create a default project
2. Add a navigation mesh and/or nav. component
3. Add a new item in navigation groups
4. Select a New group from the dropdown of the item

Expected behavior
Select one:

• Upon adding a navigation mesh or navigation component the correspoding settings should be added automatically
• Upon an attempt of adding a navigation mesh or navigation component a warning or an error that no navigation settings was found should pop up
• Dropdown of availalble items should not list items of the section that wasn't added

Start by reproducing the issue in a default Windows in-editor project using a Navigation component or NavigationMesh asset, then inspect how navigation groups are populated when GameSettings has no navigation settings. Done means selecting or adding navigation items no longer produces errors, either through automatic settings, a warning, or by hiding unavailable groups.