Occasional crash when loading a scene with particle systems utilizing triggers.

Repro steps:
1. Open SceneController scene from attached project.
2. Press Play
3. Use the right arrow to switch scenes
4. The 7th scene (Particletgest_TriggersSubEmitters_TSAMisc) occasionally crashes.

Notes:
- if scene does not crash, opening any other scene, pressing save, then repeating 1-4 often causes the project to crash.
- could not repro in 5.4.0b21; started in 5.4 staging.