Make FREE-IOBUF double-free-safe.
Make FREE-IOBUF double-free-safe.

tiago4orion/iolib,sionescu/iolib,dkochmanski/iolib,shamazmazum/iolib,tiago4orion/iolib,tiago4orion/iolib,attila-lendvai/iolib,vsedach/iolib-simple-mux,vsedach/iolib-simple-mux,deadtrickster/iolib,shamazmazum/iolib,shamazmazum/iolib,deadtrickster/iolib,sionescu/iolib,attila-lendvai/iolib,dkochmanski/iolib,deadtrickster/iolib,lispnik/iolib,attila-lendvai/iolib,dkochmanski/iolib,lispnik/iolib,sionescu/iolib,lispnik/iolib