Fix editor crash when inspecting 2 objects handled by the same plugin

Already activated plugins do not need to be added again to `editor_plugins_over`.

`fold_resource()` changes `active_plugins` and is unsafe to call while iterating
over `active_plugins`.

(cherry picked from commit 411f4763198b14d38db1afd296853996b2a5599a)

editor/editor_node.cpp

@@ -2383,22 +2383,39 @@ void EditorNode::edit_item(Object *p_object, Object *p_editing_owner) {
 			continue;
 		}
 
+		bool need_to_add = true;
+		List<EditorPropertyResource *> to_fold;
+
 		// If plugin is already associated with another owner, remove it from there first.
 		for (KeyValue<ObjectID, HashSet<EditorPlugin *>> &kv : active_plugins) {
-			if (kv.key != owner_id) {
-				EditorPropertyResource *epres = Object::cast_to<EditorPropertyResource>(ObjectDB::get_instance(kv.key));
-				if (epres && kv.value.has(plugin)) {
-					// If it's resource property editing the same resource type, fold it.
-					epres->fold_resource();
-				}
+			if (kv.key == owner_id || !kv.value.has(plugin)) {
+				continue;
+			}
+			EditorPropertyResource *epres = Object::cast_to<EditorPropertyResource>(ObjectDB::get_instance(kv.key));
+			if (epres) {
+				// If it's resource property editing the same resource type, fold it later to avoid premature modifications
+				// that may result in unsafe iteration of active_plugins.
+				to_fold.push_back(epres);
+			} else {
 				kv.value.erase(plugin);
+				need_to_add = false;
+			}
+		}
+
+		if (!need_to_add && to_fold.is_empty()) {
+			plugin->make_visible(true);
+			plugin->edit(p_object);
+		} else {
+			for (EditorPropertyResource *epres : to_fold) {
+				epres->fold_resource();
 			}
+
+			// TODO: Call the function directly once a proper priority system is implemented.
+			to_over_edit.push_back(plugin);
 		}
 
 		// Activate previously inactive plugin and edit the object.
 		active_plugins[owner_id].insert(plugin);
-		// TODO: Call the function directly once a proper priority system is implemented.
-		to_over_edit.push_back(plugin);
 	}
 
 	for (EditorPlugin *plugin : to_over_edit) {