audio: retain WASAPI clients only after initialization (#807)

## Link to GitHub Issue or related Pull Request, if one exists
Fixes #782 

## Description of change

This addresses an issue only seen on Linux + WINE.

Defer retaining WASAPI clients until `Initialize` succeeds.

Before this PR, temporary clients created during DirectShow device
capability probing were retained as active audio clients, causing
Wine/Linux crashes in DDR and popn.

Also covers IAudioClient3, dummy, ASIO, WaveOut, and null-device
initialization paths, for consistency.

## Testing
WIP

src/spice2x/hooks/audio/audio_private.h

@@ -14,4 +14,6 @@ namespace hooks::audio {
     extern std::mutex INITIALIZE_LOCK;
     extern bool VOLUME_HOOK_ENABLED;
     extern LowLatencyAudioClient *LOW_LATENCY_CLIENT;
+
+    void set_active_client(IAudioClient *client, const char *source);
 }