Fix qtyToUse in getSpecificPrice

I my FOQuantityAndDeclinaison Prices module, available on Addons store, I need to retrieve the price for a given quantity, either for simple products or for combinations of products, whatever the cart content.

I then call 
for combination price : Product::getPriceStatic($product->id, true, $id_product_attribute, 2, NULL, false, true, $qty, false, $customer->id, 0/*$id_cart*/, $id_address_vat)
for simple product : Product::getPriceStatic($product->id, $withTaxes, 0, 2, NULL, false, true, $qty, false, $customer->id, 0/*$id_cart*/, $id_address_vat)

The id_cart is set to 0, to be independant of the cart content.
The getPriceStatic must be modified to take care about the $qty given in parameter of the getPriceStatic rather than the $real_quantity.