Don't rely on $element['fid']['#value'] when adding the fields

In file_entity_inline_field_widget_process(), there's a condition that checks the $element['fid']['#value'] to determine whether or not a file has been uploaded. However, that value might not have been set depending on which order the process functions are being executed in. It's safer to rely on $element['#value']['fid'] instead, as it's always set if there's a file uploaded.