[FIX] cart total computation

Cart.vue

@@ -43,7 +43,7 @@
                 let sum = 0
 
                 for (let item of this.items) {
-                    sum = sum + ((item.price || 1) * (item.quantity || 1))
+                    sum = sum + ((item.price || 0) * (item.quantity || 0))
                 }
 
                 this.total = sum