simple ief widget on unlimited multiple field

Problem/Motivation

When using the simple IEF widget on an unlimited multiple field that is not mandatory,
an empty ief appear, if the child entity contains mandatory fields, you cannot submit the parent entity.

Proposed resolution

There is already a piece of code in InlineEntityFormSimple.php that remove the empty form for the same reason.

But it apply only with unlimited multiple field that have already entities in them

I think the empty form should only appear with mandatory field that are empty

(But i might be very wrong there might be many use cases of this module i don't see)

Remaining tasks

make a patch