The systemd user service depends on
config.xdg.configFile."hypr/hyprpaper.conf".source
for `X-Restart-Triggers`. When `cfg.settings` is the default `{}`,
this causes failure since
config.xdg.configFile."hypr/hyprpaper.conf".source
will not exist.
Making the addition conditional on `cfg.settings` actually having
content, which would mean `xdg.configFile."hypr/hyprpaper.conf"` does
exist, avoids the error.
