audio: Pass the id, not the obj, to SDL_AudioDeviceDisconnected_OnMainThread.

If a device has disconnected, and the app has quit the audio subsystem before
the queued main thread function has run, the pointer will be bogus by the time
the run occurs. So now it looks up the object from its device ID, and if the
lookup returns NULL, it returns immediately and everything works out.

Reference Issue #14856.

(which might be fixed by this or not.)

(cherry picked from commit 774728b6fffd964a79ae7cc179372736a76a633f)

src/audio/SDL_audio.c

@@ -754,8 +754,11 @@ static void SetAudioDeviceZombieFunctions(SDL_AudioDevice *device)
 // Called when a device is removed from the system, or it fails unexpectedly, from any thread, possibly even the audio device's thread.
 static void SDLCALL SDL_AudioDeviceDisconnected_OnMainThread(void *userdata)
 {
-    SDL_AudioDevice *device = (SDL_AudioDevice *) userdata;
-    SDL_assert(device != NULL);
+    const SDL_AudioDeviceID devid = (SDL_AudioDeviceID) (size_t) userdata;
+    SDL_AudioDevice *device = ObtainPhysicalAudioDevice(devid);
+    if (device == NULL) {
+        return;  // apparently it went away already.
+    }
 
     // Save off removal info in a list so we can send events for each, next
     //  time the event queue pumps, in case something tries to close a device
@@ -765,10 +768,7 @@ static void SDLCALL SDL_AudioDeviceDisconnected_OnMainThread(void *userdata)
     pending.next = NULL;
     SDL_PendingAudioDeviceEvent *pending_tail = &pending;
 
-    ObtainPhysicalAudioDeviceObj(device);
-
     SDL_LockRWLockForReading(current_audio.subsystem_rwlock);
-    const SDL_AudioDeviceID devid = device->instance_id;
     const bool is_default_device = ((devid == current_audio.default_playback_device_id) || (devid == current_audio.default_recording_device_id));
     SDL_UnlockRWLock(current_audio.subsystem_rwlock);
 
@@ -835,7 +835,7 @@ void SDL_AudioDeviceDisconnected(SDL_AudioDevice *device)
     if (device) {
         RefPhysicalAudioDevice(device);
         SDL_CompareAndSwapAtomicInt(&device->zombie, 0, 1);  // note that we're (un)dead right now, if we haven't already, but leave the event notifications for the main thread.
-        SDL_RunOnMainThread(SDL_AudioDeviceDisconnected_OnMainThread, device, false);
+        SDL_RunOnMainThread(SDL_AudioDeviceDisconnected_OnMainThread, (void *) (size_t) device->instance_id, false);
     }
 }