Actor to Track gets broken on Sequence saving when a keyframe is added

When using Actor to Lookat and adding a keyframe to the track, the references are lost to the selected Actor when saving the Sequence. This prevents the Sequence from being saved and generates a few errors.

This was reported and tested in 4.22 (CL-5660361). This was reproduced in Main 4.23 (CL-5683886). This issue was not present in 4.21 but that was before the overhaul to Sequencer.

1. Open the UE4 Editor and create a Blank Template project
2. Add a Cube or any Actor to the Level
3. Create a Level Sequence
4. Add a Cinematic Camera track to the Sequence
5. Add Actor to Track to the CineCameraActor and set it to the Cube or other Actor. CineCameraActor>Lookat Tracking Settings>Lookat>Actor to Track
6. Add a keyframe to Actor to Track
7. Save the Sequence

Results: The chain of references are lost and the sequence can't be saved

Expected: The sequence saves without error