Fix potential memory issue for applications with high throughput.
Fix potential memory issue for applications with high throughput.

iosphere/MQTTKit,NormanLeeIOS/MQTTKit,JackLeeMing/MQTTKit,nodeath/MQTTKit,nodeath/MQTTKit,mwoytowich/MQTTKit,mobile-web-messaging/MQTTKit,JackLeeMing/MQTTKit,cnbin/MQTTKit,cnbin/MQTTKit,nodeath/MQTTKit,NormanLeeIOS/MQTTKit,JackLeeMing/MQTTKit,mwoytowich/MQTTKit,jmesnil/MQTTKit,jmesnil/MQTTKit,mobile-web-messaging/MQTTKit,mobile-web-messaging/MQTTKit,cnbin/MQTTKit,Movile/MQTTKit,iosphere/MQTTKit