VFX instance leak due to asset editor not properly destroyed

How to reproduce:

1. Create a new VFX asset
2. Open Profiler
3. Try dragging VFX asset in the Scene View but release mouse elsewhere in order not to drop that asset
4. Observe Profiler's Memory section

Expected result: GameObject count does not increase

Actual result: GameObject count increases once asset being dragged to the scene

 

Note: This tricky issue was found by Gabriel