[html-formfu] pre-checked radio button

[kewei xiao]

Thanks for the hint,
for some reason, when I use fill_formfu_values, it only fills some 
value, so instead, I am using $form->get_field('')->default;

so for the radio button case, i was doing like this:

if ( $rs->item_id ) {
    $form->get_field('radioButton')->default( 'checked' );
}

but I still don't get what I expect.