Cleanup: replace tree type by tree_idname

Pull Request: https://projects.blender.org/blender/blender/pulls/139018

source/blender/editors/space_node/node_add.cc

@@ -696,8 +696,11 @@ void NODE_OT_add_collection(wmOperatorType *ot)
 static bool node_add_image_poll(bContext *C)
 {
   const SpaceNode *snode = CTX_wm_space_node(C);
-  return ED_operator_node_editable(C) &&
-         ELEM(snode->nodetree->type, NTREE_SHADER, NTREE_TEXTURE, NTREE_COMPOSIT, NTREE_GEOMETRY);
+  return ED_operator_node_editable(C) && STR_ELEM(snode->tree_idname,
+                                                  "ShaderNodeTree",
+                                                  "CompositorNodeTree",
+                                                  "TextureNodeTree",
+                                                  "GeometryNodeTree");
 }
 
 /** Node stack animation data, sorts nodes so each node is placed on top of each other. */