iPay88 acknowledge should only requery when the status is success

@bslobodin @bizla 

When iPay88 returns from an error state (such as cancellation), acknowledge returns false. They still pass us a signature, so we can still acknowledge. This fixes that by only calling `requery` when the status is success.
``success? ? requery == '00' : true`` is hurting my brain... isn't it the same as before?