Make sure marked nodes are reset on scene change

The performance improvement on the SceneTreeEditor caused the previous
state of the SceneTreeEditor::marked HashSet to matter, when it
previously was always just overwritten when markings changed. The old
code thus had no reason to ever clear the marking list.

We now make sure that whether the SceneTreeEditor is hidden or not that
when the edited scene changes we always reset the entire state of the
editor, including the marked HashSet.

editor/gui/scene_tree_editor.cpp

@@ -892,6 +892,15 @@ void SceneTreeEditor::_update_tree(bool p_scroll_to_selected) {
 		return;
 	}
 
+	Node *scene_node = get_scene_node();
+
+	if (node_cache.current_scene_node != scene_node) {
+		_reset();
+		marked.clear();
+		node_cache.current_scene_node = scene_node;
+		node_cache.force_update = true;
+	}
+
 	if (!update_when_invisible && !is_visible_in_tree()) {
 		return;
 	}
@@ -903,13 +912,6 @@ void SceneTreeEditor::_update_tree(bool p_scroll_to_selected) {
 	updating_tree = true;
 
 	last_hash = hash_djb2_one_64(0);
-	Node *scene_node = get_scene_node();
-
-	if (node_cache.current_scene_node != scene_node) {
-		_reset();
-		node_cache.current_scene_node = scene_node;
-		node_cache.force_update = true;
-	}
 
 	if (node_cache.current_scene_node) {
 		// Handle pinning/unpinning the animation player only do this once per iteration.