Fix bugs and improvements

fix payment outstanding with amount <= 0
fix payment outstanding with other payments

app/models/booking.rb

@@ -6,6 +6,8 @@ class Booking < ApplicationRecord
 
   belongs_to :dining_facility, :optional => true
   belongs_to :sale, :optional => true
+  has_one  :cashier_terminal_by_dining_facility, through: :dining_facility, source: :cashier_terminal
+  has_one  :current_shift_by_dining_facility, through: :dining_facility, source: :current_shift
   has_many :booking_orders
   has_many :orders, :through => :booking_orders
   has_many :order_items, :through => :orders do
@@ -13,7 +15,7 @@ class Booking < ApplicationRecord
       sale_items = []
       proxy_association.load_target.select(&:order_items_id).each do |order_item|
         menu_category = order_item.menu_category || OpenStruct.new(name: 'Product', code: '') #get menu category for menu items
-        
+
         sale_items << SaleItem.new({
             menu_category_name: menu_category.name,
             menu_category_code: menu_category.code,