Busy Mode: Start and end the sound frame in busy loop

Like in the main loop, the sound frame is started and ended in the
busy mode loop. This ensures that audio drivers are updated always.

doomsday/engine/portable/src/busymode.cpp

@@ -403,6 +403,9 @@ static void BusyMode_Loop(void)
 
     Garbage_Recycle();
 
+    // Make sure the audio system gets regularly updated.
+    S_StartFrame();
+
     // Post and discard all input events.
     DD_ProcessEvents(0);
     DD_ProcessSharpEvents(0);
@@ -415,7 +418,6 @@ static void BusyMode_Loop(void)
         GL_ProcessDeferredTasks(15);
     }
 
-    // Make sure the audio system gets regularly updated.
     S_EndFrame();
 
     // We accumulate time in the busy loop so that the animation of a task