fix: redis_client crashed when parsing an error redis response

[terry-xiaoyu]

Parsing failed on receiving an error response:

<<"-MISCONF Redis is configured to save RDB snapshots, but it's currently unable to persist to disk. Commands that may modify the data set are disabled, because this instance is configured to report errors during writes if RDB snapshotting fails (stop-writes-on-bgsave-error option). Please check the Redis logs for details about the RDB error.\r\n\r\n">>

[zmstone]

seems to be a bug in redis, this is perhaps a low priority fix.
redis/redis@b2061de