Hitting maxclients causes "Cannot read property 'error' of undefined"

• Version: redis: 4.0.11 node_redis 2.8.0
• Platform: Ubuntu 18.04 GCP
• Description: If you start a redis client with no_ready_check, the maxclients error from the redis server causes the client to emit a loop of bad error messages which are particularly nasty to try debug in production.

$ docker run -it -p 9379:6379 redis redis-server -- --maxclients 1
$ redis-cli -p 6379 # leave this one hanging
$ node
> var r = require('redis'); var c = r.createClient({ port: 9379, no_ready_check: true });
undefined
> TypeError: Cannot read property 'error' of undefined
    at RedisClient.return_error (.../node_modules/redis/index.js:687:21)
    at JavascriptRedisParser.returnError (.../node_modules/redis/index.js:196:18)
    at JavascriptRedisParser.execute (.../node_modules/redis-parser/lib/parser.js:572:12)
> TypeError: Cannot read property 'error' of undefined
    at RedisClient.return_error (.../node_modules/redis/index.js:687:21)
    at JavascriptRedisParser.returnError (.../node_modules/redis/index.js:196:18)
    at JavascriptRedisParser.execute (.../node_modules/redis-parser/lib/parser.js:572:12)
> TypeError: Cannot read property 'error' of undefined
    at RedisClient.return_error (.../node_modules/redis/index.js:687:21)
    at JavascriptRedisParser.returnError (.../node_modules/redis/index.js:196:18)
    at JavascriptRedisParser.execute (.../node_modules/redis-parser/lib/parser.js:572:12)

The stack trace points to index.js:687 and redis-parser/lib/parser.js:572. Reproduce the case with the Docker Redis command and Node client shown in the issue, then inspect how the maxclients response is handled when no_ready_check is enabled. Done means the client reports a stable, useful error instead of repeatedly raising TypeErrors.