WebGPURenderer: Fix `overrideMaterial` node assignments. (#32896)

src/renderers/common/Renderer.js

@@ -3195,9 +3195,9 @@ class Renderer {
 			materialOverride = true;
 
 			// store original nodes
-			materialColorNode = scene.overrideMaterial.colorNode;
-			materialDepthNode = scene.overrideMaterial.depthNode;
-			materialPositionNode = scene.overrideMaterial.positionNode;
+			materialColorNode = ( overrideMaterial.isNodeMaterial ) ? overrideMaterial.colorNode : null;
+			materialDepthNode = ( overrideMaterial.isNodeMaterial ) ? overrideMaterial.depthNode : null;
+			materialPositionNode = ( overrideMaterial.isNodeMaterial ) ? overrideMaterial.positionNode : null;
 			materialSide = scene.overrideMaterial.side;
 
 			if ( material.positionNode && material.positionNode.isNode ) {