fix issues #118 - protect from empty sub/unsub topic list
fix issues #118 - protect from empty sub/unsub topic list

sunilkumartc/ermqtt,wwezhuimeng/emqtt,kimiscircle/emqttd,jfjalburquerque/emqttd,yangchaogit/emqttd,AcmHacker/emqttd,gxbllm/emqttd,kimiscircle/emqttd,yocome/emqttd,yanyanqin/emqttd,codertrack/emqttd,lianghaivv/emqttd,kimiscircle/emqttd,wwezhuimeng/emqtt,janshahid/jmq,fengshao0907/emqttd,tempbottle/emqttd,sunilkumartc/ermqtt,fsxchen/emqttd,Inner-room/emqttd,wwezhuimeng/emqtt,guidao/emqttd,sureddy/emqttd,santuoshi/emqttd,mickelfeng/emqttd,neviim/emqttd,joaohf/emqttd,sunilkumartc/ermqtt,shaominghaoo/emqttd