Do not try to remove listener from an undefined connection
Do not try to remove listener from an undefined connection

See issue #325

linalu1/request,czardoz/request,NewGyu/request,nishant8BITS/request,kmulvey/request,robu3/request,calibr/request,zodsoft/request,sean3z/request,HAKASHUN/request,HAKASHUN/request,motopia/request,simov/request,motopia/request,IveWong/request,udp/request,NewGyu/request,mvnnn/request,Aloomaio/request,whembed197923/request,xiwc/request,request/request,djchie/request,rbramwell/request,Jonekee/request,beni55/request,ryanwholey/request,jsifuentes/request,IveWong/request,djchie/request,linalu1/request,paulomcnally/request,request/request,jzaefferer/request,xiwc/request,LoicMahieu/request,pablobrady/request,MofeLee/request,manishnakar/request,kevinburke/request,IbpTeam/node-request,robu3/request,udp/request,phillipj/request,whembed197923/request,lalitkapoor/request,Prasanna-sr/request,kevinburke/request,neo-z/request,Codelegant92/request,watson/request,jsifuentes/request,blabno/request,lalitkapoor/request,seegno-forks/request,longwenjunjie/request,xtidt/request,niklabh/request,LoicMahieu/request,chaoliu/request,calibr/request,kmulvey/request,wakermahmud/request,blabno/request,rbramwell/request,pablobrady/request,phillipj/request,bigeasy/request,zhouweiming/request,zhouweiming/request,chaoliu/request,Codelegant92/request,Aloomaio/request,kublaj/request,xtidt/request,not001praween001/request,faradayio/request,pho3nixf1re/request,wakermahmud/request,sean3z/request,longwenjunjie/request,pho3nixf1re/request,ryanwholey/request,niklabh/request,wangchi/request,kublaj/request,beni55/request,paulomcnally/request,zodsoft/request,mvnnn/request,Jonekee/request,watson/request,IbpTeam/node-request,h1bomb/request,Prasanna-sr/request,manishnakar/request,lxe/request,lxe/request,nishant8BITS/request,jzaefferer/request,seegno-forks/request,MofeLee/request,wangchi/request,not001praween001/request,simov/request,cvibhagool/request,czardoz/request,neo-z/request,h1bomb/request,cvibhagool/request,faradayio/request