fix AudioDevice crash on shutdown

src/Audio/AudioDevice.cs

@@ -42,6 +42,7 @@ namespace MoonWorks.Audio
 		private AutoResetEvent WakeSignal;
 		internal readonly object StateLock = new object();
 
+		private bool Running;
 		private bool IsDisposed;
 
 		public unsafe AudioDevice()
@@ -130,13 +131,15 @@ namespace MoonWorks.Audio
 			Thread.IsBackground = true;
 			Thread.Start();
 
+			Running = true;
+
 			TickStopwatch.Start();
 			previousTickTime = 0;
 		}
 
 		private void ThreadMain()
 		{
-			while (!IsDisposed)
+			while (Running)
 			{
 				lock (StateLock)
 				{
@@ -278,8 +281,9 @@ namespace MoonWorks.Audio
 		{
 			if (!IsDisposed)
 			{
-				lock (StateLock)
-				{
+				Running = false;
+				Thread.Join();
+
 				if (disposing)
 				{
 					foreach (var weakReference in resources)
@@ -300,7 +304,6 @@ namespace MoonWorks.Audio
 				IsDisposed = true;
 			}
 		}
-		}
 
 		~AudioDevice()
 		{

src/Audio/StaticSound.cs

@@ -311,6 +311,18 @@ namespace MoonWorks.Audio
 
 		protected override unsafe void Destroy()
 		{
+			foreach (var instance in UsedInstances)
+			{
+				instance.Free();
+			}
+
+			foreach (var instance in AvailableInstances)
+			{
+				instance.Dispose();
+			}
+
+			AvailableInstances.Clear();
+
 			if (OwnsBuffer)
 			{
 				NativeMemory.Free((void*) Handle.pAudioData);

src/Game.cs

@@ -86,12 +86,21 @@ namespace MoonWorks
 				Tick();
 			}
 
+			Logger.LogInfo("Starting shutdown sequence...");
+
+			Logger.LogInfo("Cleaning up game...");
 			Destroy();
 
+			Logger.LogInfo("Closing audio thread...");
 			AudioDevice.Dispose();
 
+			Logger.LogInfo("Unclaiming window...");
 			GraphicsDevice.UnclaimWindow(MainWindow);
+
+			Logger.LogInfo("Disposing window...");
 			MainWindow.Dispose();
+
+			Logger.LogInfo("Disposing graphics device...");
 			GraphicsDevice.Dispose();
 
 			SDL.SDL_Quit();