Scene with multiple nested SubEmitters occasionally crashes when the editor/player window is moved rapidly during the time the final SubEmitter fires.

Repro step:
1. Open ShakeToCrash scene from attached project.
2. Press play, and wait about 10 seconds (about the time many green particles appear)
3. Make sure the editor is not minimized, grab the window on top with the mouse and start moving it around, occasionally dropping it and picking it up again.
4. Editor/player crashes

Expected outcome: no crash :)

Notes:
- Editor Crash report attached (CrashReport.txt)
- Crashes also in player (attached output_log.txt)
- Couldn't reproduce crash in 5.3.1f1, crashes 5.4.0b1-3 (possibly in the alphas too)