Previously, when running the project manager, we would try to load the API assemblies from the project and fail because we were not editing any project. This would make us try to copy the prebuilt API assemblies to the project. Since there is no project, it would try to copy them to the executable location. This would fail if Godot doesn't have permissions to write to that location.
This commit fixes that by instead trying to load the prebuilt API assemblies in the first place, if running the project manager.
c9befa63d2