luvit: uv: Handle: set _closed when closed received
luvit: uv: Handle: set _closed when closed received

internally on errors luvit may close a handle. Ensure we don't double
close and cause an assert by setting self._closed on the closed signal.

sousoux/luvit,boundary/luvit,zhaozg/luvit,kaustavha/luvit,sousoux/luvit,bsn069/luvit,GabrielNicolasAvellaneda/luvit-upstream,boundary/luvit,AndrewTsao/luvit,boundary/luvit,AndrewTsao/luvit,bsn069/luvit,sousoux/luvit,GabrielNicolasAvellaneda/luvit-upstream,luvit/luvit,zhaozg/luvit,sousoux/luvit,sousoux/luvit,GabrielNicolasAvellaneda/luvit-upstream,sousoux/luvit,GabrielNicolasAvellaneda/luvit-upstream,DBarney/luvit,kaustavha/luvit,DBarney/luvit,luvit/luvit,kaustavha/luvit,connectFree/lev,rjeli/luvit,rjeli/luvit,rjeli/luvit,AndrewTsao/luvit,bsn069/luvit,rjeli/luvit,boundary/luvit,boundary/luvit,connectFree/lev,boundary/luvit,DBarney/luvit,DBarney/luvit