Fix bugs and improvements

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

app/models/employee.rb

@@ -3,6 +3,7 @@ class Employee < ApplicationRecord
   has_many :commissioners
   has_many :shit_sales
   has_one  :current_shift, -> { where.not(shift_started_at: nil).where(shift_closed_at: nil) },class_name: "ShiftSale"
+  has_one  :cashier_terminal, through: :current_shift
   belongs_to :order_queue_station
 
   validates_presence_of :name, :role