No placeholder with 'ShowOnSelect' when other options are selected

@charlot, again on the topic of Select2 tokens with 'ShowOnSelect', but a minor issue this time around.

If for each ShowOnSelect option, there is a different tokens field and the latter is used with a placeholder, the placeholder text appears only in the field that is selected after the form has loaded. When you select any other option, the placeholder is not rendered, even if the input does come with the HTML attribute placeholder and an associated value.