apport-gtk segfaults when pointed to invalid X window

[Tom Reynolds]

Pointing ubuntu-bug to a non-existing X window makes apport-gtk segfault:

myrestricteduser@ubuntu1804amd64~$ DISPLAY=:1 ubuntu-bug ubiquity
Unable to init server: Could not connect: Connection refused
Unable to init server: Could not connect: Connection refused
Segmentation fault (core dumped)
myrestricteduser@ubuntu1804amd64~$

This affects at least bionic and cosmic (crash reports were uploaded).

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: apport 2.20.9-0ubuntu7.4
ProcVersionSignature: Ubuntu 4.15.0-36.39-generic 4.15.18
Uname: Linux 4.15.0-36-generic x86_64
ApportLog:
 ERROR: apport (pid 7619) Sat Oct 20 20:09:19 2018: called for pid 7617, signal 11, core limit 0, dump mode 1
 ERROR: apport (pid 7619) Sat Oct 20 20:09:19 2018: script: /usr/share/apport/apport-gtk, interpreted by /usr/bin/python3.6 (command line "/usr/bin/python3 /usr/share/apport/apport-gtk ubiquity")
 ERROR: apport (pid 7619) Sat Oct 20 20:09:19 2018: debug: session gdbus call: (true,)

 ERROR: apport (pid 7619) Sat Oct 20 20:09:23 2018: wrote report /var/crash/_usr_share_apport_apport-gtk.1000.crash
ApportVersion: 2.20.9-0ubuntu7.4
Architecture: amd64
CrashReports:
 640:1000:120:7268297:2018-10-20 20:11:08.434944152 +0200:2018-10-20 20:11:09.434944152 +0200:/var/crash/_usr_share_apport_apport-gtk.1000.crash
 664:1000:120:0:2018-10-20 20:11:18.930962176 +0200:2018-10-20 20:11:18.930962176 +0200:/var/crash/_usr_share_apport_apport-gtk.1000.upload
CurrentDesktop: ubuntu:GNOME
Date: Sat Oct 20 20:12:03 2018
PackageArchitecture: all
SourcePackage: apport
UpgradeStatus: Upgraded to bionic on 2018-08-15 (66 days ago)