-0.00 ne 0.00. Handle both cases of ~0 when checking out to intercept and finish the transaction immediately.

docs/changelog/7.x.x.txt

@@ -1,4 +1,5 @@
 7.10.17
+ - fixed: Forced to use a PayDriver even with a balance of 0 in the cart.
 
 7.10.16
  - fixed #12121: typ-o Asset_Map.templateIdEditPoint

lib/WebGUI/Shop/Cart.pm

@@ -925,7 +925,7 @@ sub www_checkout {
         my $total = $self->calculateTotal;
         ##Handle rounding errors, and checkout immediately if the amount is 0 since
         ##at least the ITransact driver won't accept $0 checkout.
-        if (sprintf('%.2f', $total + $self->calculateShopCreditDeduction($total)) eq '0.00') {
+        if (sprintf('%.2f', abs($total + $self->calculateShopCreditDeduction($total))) eq '0.00') {
             my $transaction = WebGUI::Shop::Transaction->create($session, {cart => $self});
             $transaction->completePurchase('zero', 'success', 'success');
             $self->onCompletePurchase;