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 precheck:debian:sid:amd64 #61706
amd64 docker linux

00:00:20

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

00:02:25

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

00:02:35

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

00:01:39

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

00:02:11

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

00:16:31

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

00:17:18

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

00:04:20

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

00:04:14

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

00:04:24

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

00:01:01

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

00:01:11

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

00:00:59

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

00:00:56