Remove lambda in favor of quantifier.positive_stock

Author: spaghetticode

core/app/models/spree/fulfilment_changer.rb

@@ -144,15 +144,10 @@ def handle_stock_counts?
     end
 
     def get_available_quantity
-      positive_stock = ->(shipment) do
-        on_hand = shipment.stock_location.count_on_hand(variant)
-        on_hand.positive? ? on_hand : 0
-      end
-
       if current_stock_location != desired_stock_location
-        positive_stock.call(desired_shipment)
+        desired_location_quantifier.positive_stock
       else
-        sl_availability = positive_stock.call(current_shipment)
+        sl_availability = current_location_quantifier.positive_stock
         shipment_availability = current_shipment.inventory_units.where(variant: variant).on_hand.count
         sl_availability + shipment_availability
       end
@@ -174,11 +169,19 @@ def current_shipment_not_already_shipped
     end
 
     def enough_stock_at_desired_location
-      unless Spree::Stock::Quantifier.new(variant, desired_stock_location).can_supply?(quantity)
+      unless desired_location_quantifier.can_supply?(quantity)
         errors.add(:desired_shipment, :not_enough_stock_at_desired_location)
       end
     end
 
+    def desired_location_quantifier
+      @desired_location_quantifier ||= Spree::Stock::Quantifier.new(variant, desired_stock_location)
+    end
+
+    def current_location_quantifier
+      @current_location_quantifier ||= Spree::Stock::Quantifier.new(variant, current_stock_location)
+    end
+
     def desired_shipment_different_from_current
       if desired_shipment.id == current_shipment.id
         errors.add(:desired_shipment, :can_not_transfer_within_same_shipment)