gensalt_sha1_rn: fix read of random bytes out of bounds
gensalt_sha1_rn: fix read of random bytes out of bounds

Reported-by: Vitaly Chikunov <0d216168d6c4f83410e4fa17a56d762f8c0260fc@altlinux.org>

besser82/libxcrypt,besser82/libxcrypt,besser82/libxcrypt,besser82/libxcrypt