Use Product power tool for translation form

Hi.

I was setting up a Ubercart multilingual website, and was astonished to see that the module does not work for translation forms.

Indeed, we have linte 66 :

    // Don't change form when node is being prepared for translation
    if (!empty($form["#node"]->translation_source)) {
        return;
    }

Which means PWT is skipped in this sort of forms.

Honestly I don't know why... For me we should only not auto generate the sku in these forms as it has been already generated (but I work with a synchronizing module, so it is a bit different).