tests: Moved assert to the write place in torture_keyfiles.
tests: Moved assert to the write place in torture_keyfiles.

Found by clang-analyzer http://test.libssh.org/clang-analyzer/

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