Custom CrowdManagerClass reference is set to none when restarting the Editor

When setting a C++ class that's derived from CrowdManager as the "Crowd Manager Class", will cause the "Crowd Manager Class" value to be set to "None" when the Editor is restarted.

This issue was reported and tested in 4.21 (CL-4541578). This was reproduced in 4.20.3 (CL-4369336) and Main 4.22 (CL-4586854)

1. Open the UE4 Editor and create a Blank Template project
2. Click on File> New C++ Class...
3. Check the checkbox for Show All Classes and search for CrowdManager
4. Name the class and create it
5. In the Project Settings> Navigation System click the dropdown for Crowd Manager Class and select the C++ class that was created
6. Click Save All, close the Editor, and open the project back up

Results: "Crowd Manager Class" is set to None

Expected: "Crowd Manager Class" is set to CustomCrowdManager