feat(audio): Fix OpenAL auto detection

This commit addresses serveral bugs within the audio service where OpenAL would fail to register the output device to the mapped engine.

- Increase null safety checks for all audio backends (cubeb, sdl2, openal)
- Added failsafe for Device selection

These ensure the audio_renderer can validate calls from the OpenAL engine, Credits to Hayate Yoshida for helping Identify the issue.

Credit: Hayate Yoshida <hayate_yoshida@citron-emu.org>
Signed-off-by: Zephyron <zephyron@citron-emu.org>

src/audio_core/sink/cubeb_sink.cpp

@@ -277,7 +277,7 @@ void CubebSink::CloseStreams() {
 }
 
 f32 CubebSink::GetDeviceVolume() const {
-    if (sink_streams.empty()) {
+    if (sink_streams.empty() || !sink_streams[0]) {
         return 1.0f;
     }