CVE-2014-8132: Fixup error path in ssh_packet_kexinit()
CVE-2014-8132: Fixup error path in ssh_packet_kexinit()

Before this change, dangling pointers can be unintentionally left in the
respective next_crypto kex methods slots.  Ensure to set all slots to
NULL in the error-out path.

Signed-off-by: Jon Simons <44f878afe53efc66b76772bd845eb65944ed8232@jonsimons.org>
Reviewed-by: Andreas Schneider <5be00ddc76278cf6077f5047ca3384a88460c671@cryptomilk.org>
(cherry picked from commit 2ced24ddd67a261dc364ad4d8958c068c1671ae7)

mwgoldsmith/ssh,mwgoldsmith/ssh,mwgoldsmith/ssh,mwgoldsmith/ssh,mwgoldsmith/libssh,mwgoldsmith/libssh,mwgoldsmith/libssh,mwgoldsmith/libssh