channels: Fix integer overflow in generate_cookie().
channels: Fix integer overflow in generate_cookie().

Since the type of rnd[i] is signed char, (rnd[i] >> 4), which is
considered as arithmetic shift by gcc, could be negative, leading
to out-of-bounds read.

mwgoldsmith/libssh,Distrotech/libssh,robxu9/libssh,kedazo/libssh,sebadoom/libssh,robxu9/libssh,mwgoldsmith/libssh,pouete/libssh,mwgoldsmith/ssh,jt1/honeypot-libssh,nviennot/libssh,pouete/libssh,pouete/libssh,sebadoom/libssh,jt1/honeypot-libssh,mwgoldsmith/libssh,nviennot/libssh,robxu9/libssh,mwgoldsmith/ssh,elastichosts/libssh,taikoo/libssh,DouglasHeriot/libssh,taikoo/libssh,bigcat26/libssh-mod,jt1/honeypot-libssh,bigcat26/libssh-mod,elastichosts/libssh,DouglasHeriot/libssh,bigcat26/libssh-mod,DouglasHeriot/libssh,Distrotech/libssh,jt1/honeypot-libssh,robxu9/libssh,Distrotech/libssh,mwgoldsmith/libssh,nviennot/libssh,kedazo/libssh,wangshawn/libssh,nviennot/libssh,kedazo/libssh,elastichosts/libssh,wangshawn/libssh,wangshawn/libssh,mwgoldsmith/ssh,taikoo/libssh,kedazo/libssh,sebadoom/libssh,DouglasHeriot/libssh,wangshawn/libssh,Distrotech/libssh,sebadoom/libssh,taikoo/libssh,bigcat26/libssh-mod,pouete/libssh,mwgoldsmith/ssh