Previewing a node overrides the output of PostProceessInput0 in a Post Process Domain Material after previewing has stopped

This is not a regression. Tested in //UE5/Release-5.1 CL20979098

Previewing a node overrides the output of PostProceessInput0 in a Post Process Domain Material after previewing stops.

1. Create a new Material
2. Change the Material Domain in the Details panel to Post Process
3. Create a Scene Texture Node
4. With the node selected change the Scene Texture ID in the Details panel to Post Process Input 0
5. Connect the Color output pin to the Emissive input
6. Create a Constant3Vector node
7. Set the Y value of the Constant3Vector node to 1.0
8. Right-click the Constant3Vector node and select Start Previewing Node
9. Observe the Viewport
10. Right-click the Constant3Vector node and select Stop Previewing Node

Result: Previewing a node overrides the output of PostProceessInput0
Expected: The viewport returns to its previous state before previewing the Constant3Vector node