Add another check before session_start() and AUTO_LANGUAGE

Added checks before session_start() and AUTO_LANGUAGE to avoid errors.

These errors I found while working on the Eloquent refactor for Navigation. For example when trying to create a link.

ErrorException [ Notice ]: A session had already been started - ignoring session_start()
FCPATH/system/cms/core/MY_Controller.php [ 287 ]
282 
283         // If we've been redirected from HTTP to HTTPS on admin, ?session= will be set to maintain language
284         if ($_SERVER['SERVER_PORT'] == 443 and ! empty($_GET['session'])) {
285             session_start($_GET['session']);
286         } else {
287             session_start();
288         }
289 
290         // Lang set in URL via ?lang=something
291         if ( ! empty($_GET['lang'])) {
292             // Turn en-gb into en
	1.	{PHP internal call} » MY_Exceptions::error_handler(arguments)
	2.	FCPATH/system/cms/core/MY_Controller.php [ 287 ] » session_start()
	3.	FCPATH/system/cms/core/MY_Controller.php [ 44 ] » MY_Controller->pick_language()
	4.	FCPATH/system/cms/core/Admin_Controller.php [ 26 ] » MY_Controller->__construct()
	5.	FCPATH/system/cms/modules/navigation/controllers/admin.php [ 91 ] » Admin_Controller->__construct()
	6.	FCPATH/system/cms/libraries/MY_Form_validation.php [ 256 ] » Admin->__construct()
	7.	FCPATH/system/codeigniter/libraries/Form_validation.php [ 466 ] » MY_Form_validation->_execute(arguments)
	8.	FCPATH/system/cms/modules/navigation/controllers/admin.php [ 203 ] » CI_Form_validation->run()
	9.	{PHP internal call} » Admin->create()
	10.	FCPATH/system/codeigniter/core/CodeIgniter.php [ 356 ] » call_user_func_array(arguments)
	11.	FCPATH/index.php [ 287 ] » require_once(arguments)
Environment
ErrorException [ Notice ]: Constant AUTO_LANGUAGE already defined
FCPATH/system/cms/core/MY_Controller.php [ 363 ]
358 
359         // Set the language config. Selects the folder name from its key of 'en'
360         $CI_config->set_item('language', $config['supported_languages'][$lang]['folder']);
361 
362         // Sets a constant to use throughout ALL of CI.
363         define('AUTO_LANGUAGE', $lang);
364 
365         log_message('debug', 'Defined const AUTO_LANGUAGE: '.AUTO_LANGUAGE);
366     }
367 }
368 
	1.	{PHP internal call} » MY_Exceptions::error_handler(arguments)
	2.	FCPATH/system/cms/core/MY_Controller.php [ 363 ] » define(arguments)
	3.	FCPATH/system/cms/core/MY_Controller.php [ 44 ] » MY_Controller->pick_language()
	4.	FCPATH/system/cms/core/Admin_Controller.php [ 26 ] » MY_Controller->__construct()
	5.	FCPATH/system/cms/modules/navigation/controllers/admin.php [ 91 ] » Admin_Controller->__construct()
	6.	FCPATH/system/cms/libraries/MY_Form_validation.php [ 256 ] » Admin->__construct()
	7.	FCPATH/system/codeigniter/libraries/Form_validation.php [ 466 ] » MY_Form_validation->_execute(arguments)
	8.	FCPATH/system/cms/modules/navigation/controllers/admin.php [ 203 ] » CI_Form_validation->run()
	9.	{PHP internal call} » Admin->create()
	10.	FCPATH/system/codeigniter/core/CodeIgniter.php [ 356 ] » call_user_func_array(arguments)
	11.	FCPATH/index.php [ 287 ] » require_once(arguments)
Environment
ErrorException [ Warning ]: Cannot modify header information - headers already sent by (output started at /Users/ob/Sites/pyrocms/2.3/system/cms/core/MY_Exceptions.php:188)
FCPATH/system/codeigniter/libraries/Session/drivers/Session_cookie.php [ 722 ]
717 	 * @param	bool	HTTP protocol only flag
718 	 * @return	void
719 	 */
720 	protected function _setcookie($name, $value = '', $expire = 0, $path = '', $domain = '', $secure = FALSE, $httponly = FALSE)
721 	{
722 		setcookie($name, $value, $expire, $path, $domain, $secure, $httponly);
723 	}
724 
725 	// ------------------------------------------------------------------------
726 
727 	/**
	1.	{PHP internal call} » MY_Exceptions::error_handler(arguments)
	2.	FCPATH/system/codeigniter/libraries/Session/drivers/Session_cookie.php [ 722 ] » setcookie(arguments)
	3.	FCPATH/system/codeigniter/libraries/Session/drivers/Session_cookie.php [ 701 ] » CI_Session_cookie->_setcookie(arguments)
	4.	FCPATH/system/codeigniter/libraries/Session/drivers/Session_cookie.php [ 289 ] » CI_Session_cookie->_set_cookie()
	5.	FCPATH/system/codeigniter/libraries/Session/Session.php [ 312 ] » CI_Session_cookie->sess_save()
	6.	FCPATH/system/codeigniter/libraries/Session/Session.php [ 380 ] » CI_Session->set_userdata(arguments)
	7.	FCPATH/system/cms/modules/navigation/controllers/admin.php [ 216 ] » CI_Session->set_flashdata(arguments)
	8.	{PHP internal call} » Admin->create()
	9.	FCPATH/system/codeigniter/core/CodeIgniter.php [ 356 ] » call_user_func_array(arguments)
	10.	FCPATH/index.php [ 287 ] » require_once(arguments)