Update order_inventory_assembly.rb
Update order_inventory_assembly.rb

when adding a new line item to a complete order, the changed_attribute value for quantity returns nil. So we parse it as an integer so nil will become i and fix nil issues.

romul/spree-product-assembly,BeDepraved/spree-product-assembly,kimquy/spree-product-assembly,helloluis/spree-product-assembly,cindyward1/spree-product-assembly,helloluis/spree-product-assembly,tmedford/spree-product-assembly,glossier/spree-product-assembly,reinaris/spree-product-assembly,surfdome/spree-product-assembly,glossier/spree-product-assembly,reinaris/spree-product-assembly,agencyleroy/spree-product-assembly,surfdome/spree-product-assembly,groundctrl/spree-product-assembly,agencyleroy/spree-product-assembly,reinaris/spree-product-assembly,tmedford/spree-product-assembly,helloluis/spree-product-assembly,kimquy/spree-product-assembly,groundctrl/spree-product-assembly,agencyleroy/spree-product-assembly,spree-contrib/spree-product-assembly,kimquy/spree-product-assembly,cindyward1/spree-product-assembly,spree-contrib/spree-product-assembly,tmedford/spree-product-assembly,surfdome/spree-product-assembly,BeDepraved/spree-product-assembly,BeDepraved/spree-product-assembly,romul/spree-product-assembly,cindyward1/spree-product-assembly,romul/spree-product-assembly,groundctrl/spree-product-assembly,spree-contrib/spree-product-assembly,glossier/spree-product-assembly