gio open exits with success even though the underlying exec failed

[Mike Lundy]

This is a sort of annoyingly complex interaction, so bear with me. The observed problem is that xdg-open does not exit with a non-zero exit code when it fails to open.

```
$ unset DISPLAY
$ xdg-open http://example.com
exo-open: Cannot open display: .
$ echo $?
0
```

It turns out to not exactly be xdg-open's fault, though:
```
$ sh -x $(which xdg-open) http://example.com 2>&1 | tail -n10
+ return 0
+ open_xfce http://example.com
+ exo-open --help
+ gio help open
+ gio open http://example.com
exo-open: Cannot open display: .
+ [ 0 -eq 0 ]
+ exit_success
+ [ 0 -gt 0 ]
+ exit 0
```

So, from this we see that xdg-open uses `exo-open --help` to see if exo-open works, but it fails due to the DISPLAY, so it falls back to gio open. gio open ends up turning around and calling exo-open again, but gio swallows the exit code, so xdg-open thinks it worked.

```
$ exo-open http://example.com
exo-open: Cannot open display: .
$ echo $?
1
$ gio open http://example.com
exo-open: Cannot open display: .
$ echo $?
0
```

Versions:
$ lsb_release -rd
Description: Ubuntu 22.04.1 LTS
Release: 22.04
$ xdg-open --version
xdg-open 1.1.3
$ exo-open --version | head -n1
exo-open 4.16.3
$ gio --version
2.72.4

Specifically:
exo-utils:
  Installed: 4.16.3-1
  Candidate: 4.16.3-1
  Version table:
 *** 4.16.3-1 500
        500 http://us.archive.ubuntu.com/ubuntu jammy/universe amd64 Packages
        100 /var/lib/dpkg/status
libglib2.0-bin:
  Installed: 2.72.4-0ubuntu1
  Candidate: 2.72.4-0ubuntu1
  Version table:
 *** 2.72.4-0ubuntu1 500
        500 http://us.archive.ubuntu.com/ubuntu jammy-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     2.72.1-1 500
        500 http://us.archive.ubuntu.com/ubuntu jammy/main amd64 Packages
xdg-utils:
  Installed: 1.1.3-4.1ubuntu3~22.04.1
  Candidate: 1.1.3-4.1ubuntu3~22.04.1
  Version table:
 *** 1.1.3-4.1ubuntu3~22.04.1 500
        500 http://us.archive.ubuntu.com/ubuntu jammy-updates/main amd64 Packages
        500 http://us.archive.ubuntu.com/ubuntu jammy-updates/main i386 Packages
        100 /var/lib/dpkg/status
     1.1.3-4.1ubuntu1 500
        500 http://us.archive.ubuntu.com/ubuntu jammy/main amd64 Packages
        500 http://us.archive.ubuntu.com/ubuntu jammy/main i386 Packages

[Launchpad Janitor (janitor)]

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

[Sebastien Bacher (seb128)]

Thank you for your bug report. Indeed that seems incorrect and should be reported to https://gitlab.gnome.org/GNOME/glib/-/issues