make update_log() work if zone is not set

- update_log() is called to log update errors, but if those errors
  occur before the zone is set (for example, when returning NOTAUTH)
  it returns without logging anything.

(cherry picked from commit 395f6a14)
14 jobs for update-log-fix-v9_11 in 20 minutes and 18 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Precheck
passed #61706
amd64 docker linux
precheck:debian:sid:amd64

00:00:20

 
  Build
passed #61707
amd64 docker linux
build:centos:centos6:amd64

00:02:25

passed #61708
amd64 docker linux
build:centos:centos7:amd64

00:02:35

passed #61709
amd64 docker linux
build:debian:sid:amd64

00:01:39

passed #61710
i386 docker linux
build:debian:sid:i386

00:02:11

 
  Test
passed #61719
amd64 docker linux
install:debian:sid:amd64

00:16:31

passed #61715
amd64 docker linux
systemtest:centos:centos6:amd64

00:17:18

passed #61716
amd64 docker linux
systemtest:centos:centos7:amd64

00:04:20

passed #61717
amd64 docker linux
systemtest:debian:sid:amd64

00:04:14

passed #61718
i386 docker linux
systemtest:debian:sid:i386

00:04:24

passed #61711
amd64 docker linux
unittest:centos:centos6:amd64

00:01:01

passed #61712
amd64 docker linux
unittest:centos:centos7:amd64

00:01:11

passed #61713
amd64 docker linux
unittest:debian:sid:amd64

00:00:59

passed #61714
i386 docker linux
unittest:debian:sid:i386

00:00:56