Fix a segfault if a NULL pointer is passed to ssh_disconnect().
Fix a segfault if a NULL pointer is passed to ssh_disconnect().

kedazo/libssh,bigcat26/libssh-mod,mwgoldsmith/ssh,bigcat26/libssh-mod,wangshawn/libssh,Distrotech/libssh,elastichosts/libssh,rofl0r/libssh,pouete/libssh,taikoo/libssh,miloj/libssh-v0.5,jahrome/libssh,DouglasHeriot/libssh,mwgoldsmith/libssh,Distrotech/libssh,mwgoldsmith/libssh,miloj/libssh-v0.5,robxu9/libssh,kedazo/libssh,DouglasHeriot/libssh,taikoo/libssh,jt1/honeypot-libssh,mwgoldsmith/ssh,substack/libssh,bigcat26/libssh-mod,nviennot/libssh,miloj/libssh-v0.5,nviennot/libssh,substack/libssh,wangshawn/libssh,jt1/honeypot-libssh,elastichosts/libssh,jt1/honeypot-libssh,robxu9/libssh,mwgoldsmith/libssh,jahrome/libssh,taikoo/libssh,kedazo/libssh,mwgoldsmith/libssh,sebadoom/libssh,wangshawn/libssh,nviennot/libssh,jt1/honeypot-libssh,rofl0r/libssh,sebadoom/libssh,substack/libssh,sebadoom/libssh,Distrotech/libssh,Distrotech/libssh,elastichosts/libssh,pouete/libssh,rofl0r/libssh,rofl0r/libssh,bigcat26/libssh-mod,miloj/libssh-v0.5,robxu9/libssh,kedazo/libssh,pouete/libssh,DouglasHeriot/libssh,jahrome/libssh,DouglasHeriot/libssh,jahrome/libssh,pouete/libssh,sebadoom/libssh,taikoo/libssh,nviennot/libssh,mwgoldsmith/ssh,wangshawn/libssh,mwgoldsmith/ssh,robxu9/libssh,substack/libssh