Adding an employee when a record is already selected

[KyleChaplin]

When selecting an employee in the employee table their information populates the text fields automatically, if the user then presses the “Add” button an error is displayed in the console, no new record is added and the application does not crash. This is due to the system attempting to add an employee that already exists, in order to fix this, I will add a check and display an error message to the user if they attempt to do this.

[KyleChaplin]

A simple check has been added to ensure that someone does not try to add an existing employee to the database.