Calling TableView.queryAccessibleAttribute(AccessibleAttribute.FOCUS_ITEM); with a null focus model results in an NPE

added to TableViewTest:
```
    @Ignore("JDK-8296413")
    @Test
    public void testQueryAccessibleAttributeFocusItemWithNullFocusModel() {
        table.getItems().addAll("1", "2");
        table.setFocusModel(null);

        stageLoader = new StageLoader(table);

        Object result = table.queryAccessibleAttribute(AccessibleAttribute.FOCUS_ITEM);

        assertNull(result);
    }
```

ALSO
- see if TreeTableView has the same issue
- check whether other Controls throw exceptions from queryAccessibleAttribute(), trying all possible AccessibleAttribute values