Merge pull request #93292 from rune-scape/singleton-cleanup

Fix missing cleanup and null checks for various singletons

editor/editor_node.cpp

@@ -3539,7 +3539,7 @@ void EditorNode::add_extension_editor_plugin(const StringName &p_class_name) {
 
 void EditorNode::remove_extension_editor_plugin(const StringName &p_class_name) {
 	// If we're exiting, the editor plugins will get cleaned up anyway, so don't do anything.
-	if (singleton->exiting) {
+	if (!singleton || singleton->exiting) {
 		return;
 	}