Use $selected_date instead of its equivalent coming from the POST (#469).

(cherry picked from commit 36dbde8)

src/application/controllers/Appointments.php

@@ -1016,7 +1016,7 @@ class Appointments extends CI_Controller {
 
                     if ($service['attendants_number'] > 1)
                     {
-                        $available_hours = $this->_get_multiple_attendants_hours($this->input->post('selected_date'), $service,
+                        $available_hours = $this->_get_multiple_attendants_hours($selected_date, $service,
                             $provider);
                     }