Throw an exception when a user tries to view a request that does not exist.

application/modules/requests/controllers/ViewController.php

@@ -12,6 +12,9 @@ class Requests_ViewController extends App_Controller_Action
 		
 		$session = new Zend_Session_Namespace('My Requests');
 		$request = Requests_RequestModel::find($id);
+		if (!$request) {
+			throw new Zend_Exception('The specified request does not exist.');
+		}
         $user = Auth_UserModel::findCurrentUser();
         
         $viewTime = Requests_ViewTimeModel::findByUserAndRequest($user, $request);