fix a bug when subscriber is called after unsubscribing
fix a bug when subscriber is called after unsubscribing

... after unsubscribing from another subscriber (rel #119)

AgentME/kefir,elsehow/kefir,pixelpicosean/kefir,lautis/kefir,elsehow/kefir,AyaMorisawa/kefir,pixelpicosean/kefir,hsavit1/kefir,kelsadita/kefir,lautis/kefir,kelsadita/kefir,hsavit1/kefir,AgentME/kefir,AyaMorisawa/kefir