[APU] Fix audio crashes during shutdown

src/xenia/apu/audio_system.cc

@@ -178,6 +178,25 @@ void AudioSystem::Shutdown() {
     worker_thread_->Wait(0, 0, 0, nullptr);
     worker_thread_.reset();
   }
+
+  // Unregister all active clients to shut down their audio drivers before
+  // the semaphores are destroyed with this AudioSystem.
+  {
+    auto global_lock = global_critical_region_.Acquire();
+    for (size_t i = 0; i < kMaximumClientCount; ++i) {
+      if (clients_[i].in_use) {
+        DestroyDriver(clients_[i].driver);
+        if (clients_[i].wrapped_callback_arg) {
+          memory()->SystemHeapFree(clients_[i].wrapped_callback_arg);
+        }
+        clients_[i].driver = nullptr;
+        clients_[i].callback = 0;
+        clients_[i].callback_arg = 0;
+        clients_[i].wrapped_callback_arg = 0;
+        clients_[i].in_use = false;
+      }
+    }
+  }
 }
 
 X_STATUS AudioSystem::RegisterClient(uint32_t callback, uint32_t callback_arg,