Decrement connected client count rather than show disconnected
Decrement connected client count rather than show disconnected

to close #1577

mw75/node-red,Kazuki-Nakanishi/node-red,Kazuki-Nakanishi/node-red,btsimonh/node-red,rdrm2014/node-red,node-red/node-red,namgk/node-red,rdrm2014/node-red,btsimonh/node-red,rdrm2014/node-red,node-red/node-red,HiroyasuNishiyama/node-red,mw75/node-red,HiroyasuNishiyama/node-red,rdrm2014/node-red,Kazuki-Nakanishi/node-red,mw75/node-red,mw75/node-red,HiroyasuNishiyama/node-red,btsimonh/node-red,namgk/node-red,node-red/node-red,Kazuki-Nakanishi/node-red