Cache_redis, delete() method: Try to remove a key from Redis auxilary set only when the corresponding value is really deleted.
diff --git a/system/libraries/Cache/drivers/Cache_redis.php b/system/libraries/Cache/drivers/Cache_redis.php
index 2037878..b5387c0 100644
--- a/system/libraries/Cache/drivers/Cache_redis.php
+++ b/system/libraries/Cache/drivers/Cache_redis.php
@@ -134,10 +134,13 @@
 	 */
 	public function delete($key)
 	{
-		// This is for not leaving garbage keys within the Redis auxilary set.
-		$this->_redis->sRemove('_ci_redis_serialized', $key);
+		if ($result = ($this->_redis->delete($key) === 1))
+		{
+			// This is for not leaving garbage keys within the Redis auxilary set.
+			$this->_redis->sRemove('_ci_redis_serialized', $key);
+		}
 
-		return ($this->_redis->delete($key) === 1);
+		return $result;
 	}
 
 	// ------------------------------------------------------------------------