Fix crash when trying to create bones from Control

(cherry picked from commit 6a120107b330c5859f934080fc4dca1c83c3a6ab)

editor/plugins/canvas_item_editor_plugin.cpp

@@ -4594,6 +4594,9 @@ void CanvasItemEditor::_popup_callback(int p_op) {
 			undo_redo->create_action(TTR("Create Custom Bone2D(s) from Node(s)"));
 			for (const KeyValue<Node *, Object *> &E : selection) {
 				Node2D *n2d = Object::cast_to<Node2D>(E.key);
+				if (!n2d) {
+					continue;
+				}
 
 				Bone2D *new_bone = memnew(Bone2D);
 				String new_bone_name = n2d->get_name();