Update User Selection Logic to Compare IDs Instead of Names in SelectUserTableViewController

[banghuazhao]

In Chapter 12: Creating a Simple iPhone App, Part 1, it is recommended to compare user IDs in SelectUserTableViewController instead of name, as name may not be unique and could result in multiple users being selected.

The provided Swift code comparison can then be updated as follows:

    if user.id == selectedUser.id {
      cell.accessoryType = .checkmark
    } else {
      cell.accessoryType = .none
    }