Fix crash when no callback is defined
Fix crash when no callback is defined

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