pki: Make sure sig is not used unintialized.
pki: Make sure sig is not used unintialized.

BUG: https://red.libssh.org/issues/167

Signed-off-by: Andreas Schneider <5be00ddc76278cf6077f5047ca3384a88460c671@cryptomilk.org>

DouglasHeriot/libssh,kedazo/libssh,robxu9/libssh,mwgoldsmith/libssh,nviennot/libssh,kedazo/libssh,sebadoom/libssh,robxu9/libssh,pouete/libssh,mwgoldsmith/libssh,mwgoldsmith/ssh,robxu9/libssh,nviennot/libssh,Distrotech/libssh,Distrotech/libssh,wangshawn/libssh,taikoo/libssh,taikoo/libssh,mwgoldsmith/ssh,mwgoldsmith/ssh,DouglasHeriot/libssh,wangshawn/libssh,pouete/libssh,nviennot/libssh,wangshawn/libssh,DouglasHeriot/libssh,mwgoldsmith/libssh,robxu9/libssh,mwgoldsmith/libssh,Distrotech/libssh,taikoo/libssh,taikoo/libssh,mwgoldsmith/ssh,sebadoom/libssh,DouglasHeriot/libssh,sebadoom/libssh,kedazo/libssh,Distrotech/libssh,nviennot/libssh,sebadoom/libssh,kedazo/libssh,pouete/libssh,pouete/libssh,wangshawn/libssh