xdg-desktop-portal crashed with SIGSEGV in export_portal_implementation -> on_bus_acquired -> connection_get_cb -> g_task_return_now -> g_task_return

[Jean-Baptiste Lallement]

Test Case:
1. Boot desktop image to the live session and wait.

https://errors.ubuntu.com/problem/70a7581dd245188e74367f2c31a505b664b972c9

ProblemType: Crash
DistroRelease: Ubuntu 18.10
Package: xdg-desktop-portal 1.0.2-1
ProcVersionSignature: Ubuntu 4.18.0-8.9-generic 4.18.7
Uname: Linux 4.18.0-8-generic x86_64
ApportVersion: 2.20.10-0ubuntu11
Architecture: amd64
CasperVersion: 1.396
CurrentDesktop: ubuntu:GNOME
Date: Fri Oct 5 18:32:18 2018
ExecutablePath: /usr/libexec/xdg-desktop-portal
LiveMediaBuild: Ubuntu 18.10 "Cosmic Cuttlefish" - Beta amd64 (20181005)
ProcCmdline: /usr/libexec/xdg-desktop-portal
ProcEnviron:
 LANG=C.UTF-8
 PATH=(custom, no user)
 SHELL=/bin/bash
 XDG_RUNTIME_DIR=<set>
SegvAnalysis:
 Segfault happened at: 0x55e121607ff0: mov 0x8(%rax),%rcx
 PC (0x55e121607ff0) ok
 source "0x8(%rax)" (0x00000008) not located in a known VMA region (needed readable region)!
 destination "%rcx" ok
SegvReason: reading NULL VMA
Signal: 11
SourcePackage: xdg-desktop-portal
StacktraceTop:
 ?? ()
 ?? ()
 ?? () from /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0
 ?? () from /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0
 ?? () from /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0
Title: xdg-desktop-portal crashed with SIGSEGV
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo

[Apport retracing service (apport)]

StacktraceTop:
 export_portal_implementation (connection=0x55e12212f030, skeleton=0x0) at src/xdg-desktop-portal.c:352
 on_bus_acquired (connection=0x55e12212f030, name=<optimized out>, user_data=<optimized out>) at src/xdg-desktop-portal.c:384
 connection_get_cb (source_object=<optimized out>, res=0x55e12214c910, user_data=0x55e12214abd0) at ../../../../gio/gdbusnameowning.c:487
 g_task_return_now (task=0x55e12214c910) at ../../../../gio/gtask.c:1148
 g_task_return (task=0x55e12214c910, type=<optimized out>) at ../../../../gio/gtask.c:1206

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.