ntpviz: Also look in PREFIX for liberation font.

This looks in PREFIX before /usr, on the theory that any locally
installed version should be preferable.

TESTED:
With PREFIX set to /opt/local, now finds MacPorts-installed liberation
font.  The fallback also worked, so the only real effect in this case
is to get rid of the warning.
67 jobs for master in 5 minutes and 48 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #712557816
gitlab-org
AsciiDoc-3-Fedora

00:02:39

passed #712557817
gitlab-org
AsciiDoc-classic2-Alpine

00:01:58

passed #712557818
gitlab-org
AsciiDoc-classic3-Alpine

00:01:50

passed #712557819
gitlab-org
AsciiDoc-no

00:00:47

passed #712557820
gitlab-org
AsciiDoc-py3-Ubuntu

00:04:04

passed #712557812
gitlab-org
alpine-basic

00:00:49

passed #712557814
gitlab-org
alpine-edge-basic

00:00:50

passed #712557815
gitlab-org
alpine-edge-refclocks

00:00:54

passed #712557813
gitlab-org
alpine-refclocks

00:00:56

passed #712557839
gitlab-org
centos-latest-basic

00:00:56

passed #712557840
gitlab-org
centos-latest-refclocks

00:01:00

passed #712557848
gitlab-org
clang-basic

00:01:15

passed #712557849
gitlab-org
clang-refclocks

00:01:14

passed #712557865
ubuntu-1604-lts
cross-build

00:00:39

passed #712557821
gitlab-org
debian-oldstable-basic

00:00:47

passed #712557822
gitlab-org
debian-oldstable-refclocks

00:00:49

passed #712557823
gitlab-org
debian-stable-basic

00:00:56

passed #712557857
gitlab-org
debian-stable-basic-32bit

00:00:55

passed #712557862
gitlab-org
debian-stable-mDNS-basic

00:00:59

passed #712557863
gitlab-org
debian-stable-mDNS-refclocks

00:00:59

passed #712557824
gitlab-org
debian-stable-refclocks

00:01:00

passed #712557859
gitlab-org
debian-stable-refclocks-32bit

00:01:00

passed #712557825
gitlab-org
debian-testing-basic

00:00:52

passed #712557826
gitlab-org
debian-testing-refclocks

00:00:41

passed #712557827
gitlab-org
debian-unstable-basic

00:00:53

passed #712557828
gitlab-org
debian-unstable-refclocks

00:00:59

passed #712557882
gitlab-org
feature-classic-mode

00:00:55

passed #712557884
gitlab-org
feature-debug

00:00:57

passed #712557885
gitlab-org
feature-debug-gdb

00:00:57

passed #712557886
gitlab-org
feature-debug-timing

00:00:53

passed #712557887
gitlab-org
feature-disable-droproot

00:00:53

passed #712557888
gitlab-org
feature-early-droproot

00:00:53

passed #712557889
gitlab-org
feature-leap-smear

00:00:54

passed #712557890
gitlab-org
feature-mssntp

00:00:54

passed #712557883
gitlab-org
feature-seccomp

00:00:43

passed #712557841
gitlab-org
fedora-latest-basic

00:00:57

passed #712557842
gitlab-org
fedora-latest-refclocks

00:01:05

passed #712557843
gitlab-org
fedora-rawhide-basic

00:00:58

passed #712557844
gitlab-org
fedora-rawhide-refclocks

00:01:00

passed #712557845
gitlab-org
fedora-rawhide-refclocks-gpsd

00:01:04

passed #712557835
freebsd-11
freebsd-11-basic

00:01:37

passed #712557836
freebsd-11
freebsd-11-refclocks

00:01:46

passed #712557837
freebsd-12
freebsd-12-basic

00:01:53

passed #712557838
freebsd-12
freebsd-12-refclocks

00:02:13

passed #712557868
gitlab-org
gentoo-basic

00:01:53

passed #712557873
gitlab-org
gentoo-hardened-basic

00:01:49

passed #712557875
gitlab-org
gentoo-hardened-refclocks

00:01:55

passed #712557870
gitlab-org
gentoo-refclocks

00:01:54

passed #712557877
macos
macos-basic

00:01:04

passed #712557879
macos
macos-refclocks

00:01:04

passed #712557850
gitlab-org
openSUSE-leap-basic

00:00:39

passed #712557851
gitlab-org
openSUSE-leap-refclocks

00:00:58

passed #712557852
gitlab-org
openSUSE-tumbleweed-basic

00:00:56

passed #712557853
gitlab-org
openSUSE-tumbleweed-refclocks

00:01:07

passed #712557847
gitlab-org
python-coverage

00:01:30

94.0%
passed #712557846
gitlab-org
python3-rc

00:01:15

passed #712557833
gitlab-org
ubuntu-devel-basic

00:00:43

passed #712557834
gitlab-org
ubuntu-devel-refclocks

00:01:01

passed #712557829
gitlab-org
ubuntu-latest-basic

00:00:53

passed #712557830
gitlab-org
ubuntu-latest-refclocks

00:01:00

passed #712557831
gitlab-org
ubuntu-rolling-basic

00:00:53

passed #712557832
gitlab-org
ubuntu-rolling-refclocks

00:00:52

 
  Test
passed #712557895
bandit-sast

00:00:35

passed #712557892
code_quality

00:05:47

passed #712557897
eslint-sast

00:00:34

passed #712557899
flawfinder-sast

00:00:29

passed #712557901
license_scanning

00:02:06