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_12 in 21 minutes and 24 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Precheck
passed #61692
amd64 docker linux
precheck:debian:sid:amd64

00:00:16

 
  Build
passed #61693
amd64 docker linux
build:centos:centos6:amd64

00:02:51

passed #61694
amd64 docker linux
build:centos:centos7:amd64

00:02:59

passed #61695
amd64 docker linux
build:debian:sid:amd64

00:02:04

passed #61696
i386 docker linux
build:debian:sid:i386

00:02:13

 
  Test
passed #61705
amd64 docker linux
install:debian:sid:amd64

00:02:19

passed #61701
amd64 docker linux
systemtest:centos:centos6:amd64

00:04:57

passed #61702
amd64 docker linux
systemtest:centos:centos7:amd64

00:04:53

passed #61703
amd64 docker linux
systemtest:debian:sid:amd64

00:18:07

passed #61704
i386 docker linux
systemtest:debian:sid:i386

00:04:40

passed #61697
amd64 docker linux
unittest:centos:centos6:amd64

00:01:03

passed #61698
amd64 docker linux
unittest:centos:centos7:amd64

00:01:02

passed #61699
amd64 docker linux
unittest:debian:sid:amd64

00:00:54

passed #61700
i386 docker linux
unittest:debian:sid:i386

00:00:55