[Bug]: `Backlight::new` returns early instead of using dbus

[avalsch]

Steps for reproducing the issue

Run wluma with a backlight configured and without write permissions (no udev rule).

What is the buggy behavior?

wluma outputs the following warning: Skipping 'eDP-1' as it might be disconnected: Permission denied (os error 13)

What is the expected behavior?

Brightness::new should correctly fall back to using dbus instead of returning early.

Logs

RUST_LOG=debug wluma
[2024-02-29T16:34:40Z DEBUG wluma] Using Config {
        als: Webcam {
            video: 0,
            thresholds: {
                0: "night",
                60: "bright",
                15: "dark",
                45: "normal",
                30: "dim",
                75: "outdoors",
            },
        },
        output: [
            Backlight(
                BacklightOutput {
                    name: "eDP-1",
                    path: "/sys/class/backlight/intel_backlight",
                    capturer: Wlroots,
                    min_brightness: 1,
                },
            ),
        ],
    }
[2024-02-29T16:34:40Z WARN  wluma] Skipping 'eDP-1' as it might be disconnected: Permission denied (os error 13)
[2024-02-29T16:34:40Z INFO  wluma] Continue adjusting brightness and wluma will learn your preference over time.

Version

Built from source using the latest git.

Environment

lsb_release -a; uname -a; pgrep -l sway; pacman -Q | egrep "(wlroots|vulkan|sway|clang|rust)"; dpkg -l | egrep "(wlroots|vulkan|sway|clang|rust)"
LSB Version:    n/a
Distributor ID: Arch
Description:    Arch Linux
Release:    rolling
Codename:   n/a
Linux wyrda 6.7.6-arch1-1 #1 SMP PREEMPT_DYNAMIC Fri, 23 Feb 2024 16:31:48 +0000 x86_64 GNU/Linux
84120 swaybg
84129 swayidle
egrep: warning: egrep is obsolescent; using grep -E
clang 16.0.6-2
rustup 1.26.0-5
swaybg 1.2.0-1
swayidle 1.8.0-1
swaylock-effects 1.7.0.0-4
vulkan-headers 1:1.3.276-1
vulkan-icd-loader 1.3.276-1
vulkan-intel 1:24.0.1-1
vulkan-tools 1.3.269-1
vulkan-validation-layers 1.3.275-1
wlroots 0.17.1-1
egrep: warning: egrep is obsolescent; using grep -E