QmlDesigner.StatesEditor: fix warnings

Task-number: QTCREATORBUG-10955
Change-Id: I6a382ed7935463c71103ca51a0a5b4822ab8cfc0
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>