Bug#1034878: meld gives python traceback if run as root

[Wookey]

Package: meld
Version: 3.22.0-2
Severity: normal

I change to root inorder to be able to access some files to diff and ran meld. I got the following traceback:
root at mongol:~# meld
Traceback (most recent call last):
  File "/usr/bin/meld", line 463, in <module>
    sys.exit(main())
             ^^^^^^
  File "/usr/bin/meld", line 458, in main
    setup_settings()
  File "/usr/bin/meld", line 317, in setup_settings
    meld.settings.create_settings()
  File "/usr/lib/python3/dist-packages/meld/settings.py", line 124, in create_settings
    _meldsettings = MeldSettings()
                    ^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/meld/settings.py", line 39, in __init__
    self.on_setting_changed(settings, 'prefer-dark-theme')
  File "/usr/lib/python3/dist-packages/meld/settings.py", line 58, in on_setting_changed
    gtk_settings.props.gtk_application_prefer_dark_theme = prefer_dark
    ^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'props'

~#meld boot0 boot1
(i.e supplying filenames) gave the same output.

meld runs fine when run as the desktop user
It should deal more elegantly with this situation.

--
Wookey