Minor - UEFN crash if you preview a sorting node

[Wertandrew]

Repro:

1. Make a new material
2. Press 3 and click once to add a Float 3
3. Connect it to roughness
4. Double click on the connection line to make a sorting node
5. Right click on it >> preview node
6. UEFN will crash
   
   
   
   UnrealEditorFortnite.log (4.0 MB)