refactor: improves exception handling

* ensure todoPersistence object is not null on all paths
* output ignored exceptions to std err

todolist/fxui/src/main/java/todolist/ui/TodoAppController.java

@@ -85,9 +85,12 @@ public class TodoAppController {
         reader = new StringReader(todoListWithTwoItems);
       }
       try {
+        if (todoPersistence != null) {
           todoModel = todoPersistence.readTodoModel(reader);
+        }   
       } catch (IOException e) {
         // ignore
+        System.err.println(e.toString());
       } finally {
         try {
           if (reader != null) {
@@ -95,6 +98,7 @@ public class TodoAppController {
           }
         } catch (IOException e) {
           // ignore
+          System.err.println(e.toString());
         }
       }
     }