fix #572 crash when switching mods while playing music

OpenRA.Game/Game.cs

@@ -266,9 +266,11 @@ namespace OpenRA
 			var mm = mods.Where( m => Mod.AllMods.ContainsKey( m ) ).ToArray();
 			Console.WriteLine("Loading mods: {0}",string.Join(",",mm));
 			Settings.Game.Mods = mm;
-			Settings.Save();
-			
-			Sound.Initialize();
+			Settings.Save();
+
+			Sound.StopMusic();
+			Sound.StopVideo();
+			Sound.Initialize();
 			
 			modData = new ModData( mm );
 			modData.LoadInitialAssets();