Update price checking for negative prices

Author: hoffmabc

core/listings.go

@@ -666,7 +666,10 @@ func (n *OpenBazaarNode) SetPriceOnListings(percentage float64) error {
 			oldSL := repo.NewSignedListingFromProtobuf(signedProto)
 			l := oldSL.GetListing()
 
-			l.SetPrices(percentage)
+			err = l.SetPrices(percentage)
+			if err != nil {
+				return err
+			}
 
 			lb, err := l.MarshalJSON()
 			if err != nil {

repo/listing.go

@@ -516,7 +516,13 @@ func (l *Listing) SetPrices(percentage float64) error {
 	newPrice := new(big.Float).Mul(currentPrice, floatFactor)
 	newPriceInt, _ := newPrice.Int(nil)
 
-	l.listingProto.Item.BigPrice = newPriceInt.String()
+	// Check if new price is negative
+	zeroInt, _ := new(big.Int).SetString("0", 10)
+	if newPriceInt.Cmp(zeroInt) == -1 {
+		l.listingProto.Item.BigPrice = "1"
+	} else {
+		l.listingProto.Item.BigPrice = newPriceInt.String()
+	}
 
 	return nil
 }