Manually implement PR bcit-ci#2033

Check for an empty encryption_key shouldn't use strict comparison.

system/libraries/Session/drivers/Session_cookie.php

@@ -219,7 +219,7 @@ protected function initialize()
 				: $this->CI->config->item($key);
 		}
 
-		if ($this->encryption_key === '')
+		if (empty($this->encryption_key))
 		{
 			show_error('In order to use the Cookie Session driver you are required to set an encryption key in your config file.');
 		}