fix(picker): handle prop properties which does not define getOpacity

depending on the prop type being tested for picking, the property can be different classes. e.g.
vtkVolumeProperty which does not define a getOpacity method.

Sources/Rendering/Core/Picker/index.js

@@ -112,10 +112,17 @@ function vtkPicker(publicAPI, model) {
     // Note that only vtkProp3D's can be picked by vtkPicker.
     props.forEach((prop) => {
       const mapper = prop.getMapper();
+
+      let propIsNotFullyTranslucent = true;
+
+      if (prop.getProperty && prop.getProperty().getOpacity) {
+        propIsNotFullyTranslucent = prop.getProperty().getOpacity() > 0.0;
+      }
+
       const pickable =
         prop.getNestedPickable() &&
         prop.getNestedVisibility() &&
-        prop.getProperty().getOpacity() > 0.0;
+        propIsNotFullyTranslucent;
 
       if (!pickable) {
         // prop cannot be picked