wf-panel & wf-locker: Handle empty states in Volume/Mixer widgets (missing inputs, empty streams)

[mrfoggg]

Summary

Currently, when certain audio categories are empty (e.g., no input devices connected or no active media streams playing), both wf-panel (Volume Mixer popup) and wf-locker (Volume widget) render empty, blank UI containers without feedback or adaptivity.

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Proposal & Desired Behavior

1. wf-panel Volume Mixer Popup

In the Volume Mixer popup (which consists of three columns: Output Devices, Input Devices, and Audio Streams):

• Empty Input/Output Devices: If no input (or output) devices are available, display a clear label in the respective column:
  • "No available output devices" / "Нет доступных устройств вывода"
  • "No available input devices" / "Нет доступных устройств ввода"
• Empty Audio Streams: If no audio streams/apps are playing:
  • Display a label like "No active playback" / "Ничего не воспроизводится".

Currently, the "Input Devices" heading is shown with a completely empty box underneath, which looks broken.

2. wf-locker Volume Widget

On the lockscreen, the Volume widget renders two side-by-side rectangular sections (Left: Input / Microphone, Right: Output / Speaker).

• Adaptive visibility: If no input device (microphone) is detected/present in the system, do not render the empty left box.
• The widget should dynamically adjust to display only the available section (single box for Output), rather than leaving an empty, confusing placeholder box on the screen.

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System Context

• OS: Void Linux
• Component: wf-panel & wf-locker (wf-shell)
• Audio Server: PipeWire / PulseAudio (via GVC)

[AKArien]

* **Empty Input/Output Devices:** If no input (or output) devices are available, display a clear label in the respective column:
  
  * _"No available output devices"_ / _"Нет доступных устройств вывода"_
  * _"No available input devices"_ / _"Нет доступных устройств ввода"_

* **Empty Audio Streams:** If no audio streams/apps are playing:
  
  * Display a label like _"No active playback"_ / _"Ничего не воспроизводится"_.

Also, another alternative could be to entirely hide the section if there is nothing to be shown ; just food for thought for whoever will eventually do this.