Fix Redis session driver returning success on failed connection.

The open() method in Session_redis_driver returns $this->_success even when Redis::connect() fails (the else branch on a failed connection). This causes PHP's session_start() to believe the handler is ready, but subsequent read() calls fail, producing:

session_start(): Failed to read session data: user (path: /var/lib/php/sessions)

This was originally reported and fixed in the upstream bcit-ci/CodeIgniter repo:

Issue: bcit-ci#5779
PR: bcit-ci#5781
The fix was merged into CI3 for the 3.1.11 milestone but appears to have been lost when the 3.2.0-dev branch was created, which this fork is based on.

The fix changes the failed-connection else branch to log an error and fall through to return $this->_failure instead of incorrectly returning $this->_success.

Author: czirosan

system/libraries/Session/drivers/Session_redis_driver.php

@@ -217,9 +217,7 @@ public function open($save_path, $name)
 		}
 		else
 		{
-			$this->_redis = $redis;
-			$this->php5_validate_id();
-			return $this->_success;
+			log_message('error', 'Session: Unable to connect to Redis with the configured settings.');
 		}
 
 		return $this->_failure;