status-page: Hide title/description when they're empty or NULL

Fixes GNOME/libhandy#387
11 jobs for status_page_hide_description in 14 minutes and 1 second (queued for 1 second)
Status Name Job ID Coverage
  Build
passed api-visibility #1046941

00:00:17

passed build-debian-clang #1046943

00:02:15

passed build-debian-gcc #1046942

00:02:46

passed build-fedora-gcc #1046944

00:04:03

passed build-flatpak #1046945
flatpak

00:02:40

passed build-flatpak-glade #1046946
flatpak

00:05:11

 
  Test+Docs
passed build-gtkdoc #1046947

00:02:39

passed unit-test #1046948

00:02:38

46.1%
 
  Package
passed package-debian-buster #1046949

00:03:30

 
  Test Package
passed autopkgtest-debian-buster-package #1046950

00:02:38

passed lintian-debian-buster-package #1046951

00:00:53