Hides error_panel of state machine on the first time.

editor/plugins/animation_state_machine_editor.cpp

@@ -1340,6 +1340,7 @@ AnimationNodeStateMachineEditor::AnimationNodeStateMachineEditor() {
 	add_child(error_panel);
 	error_label = memnew(Label);
 	error_panel->add_child(error_label);
+	error_panel->hide();
 
 	undo_redo = EditorNode::get_singleton()->get_undo_redo();