Alt+tab fix for ca9109be75 - call sound IdleTask in Atlas and swap buffers only once in Atlas.

- ca9109be75 moved SwapBuffers inside Render - this makes Atlas call it
twice in a row which might behave oddly (did not seem to though) and
anyways was wasteful.
- ca9109be75 moved IdleTask from the sound manager outside of Render.
This means atlas never called IdleTask, and this broke sounds after a
few seconds.

Reviewed By: Angen
Differential Revision: https://code.wildfiregames.com/D2029
This was SVN commit r22544.

source/ps/Game.cpp

@@ -1,4 +1,4 @@
-/* Copyright (C) 2018 Wildfire Games.
+/* Copyright (C) 2019 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -409,12 +409,7 @@ void CGame::Update(const double deltaRealTime, bool doInterpolate)
 	}
 
 	if (doInterpolate)
-	{
 		m_TurnManager->Interpolate(deltaSimTime, deltaRealTime);
-
-		if ( g_SoundManager )
-			g_SoundManager->IdleTask();
-	}
 }
 
 void CGame::Interpolate(float simFrameLength, float realFrameLength)