Merge pull request #4491 from roastduck/develop

[ci skip] Clean current lock key on close() in redis session driver
diff --git a/system/libraries/Session/drivers/Session_redis_driver.php b/system/libraries/Session/drivers/Session_redis_driver.php
index ad95309..7b7951f 100644
--- a/system/libraries/Session/drivers/Session_redis_driver.php
+++ b/system/libraries/Session/drivers/Session_redis_driver.php
@@ -254,7 +254,7 @@
 			try {
 				if ($this->_redis->ping() === '+PONG')
 				{
-					isset($this->_lock_key) && $this->_redis->delete($this->_lock_key);
+					$this->_release_lock();
 					if ($this->_redis->close() === $this->_failure)
 					{
 						return $this->_failure;