BugFix: correctly wait for Mixer to save file on exit

On the way, also improved Connection Manager ending properly.

main.cpp

@@ -162,6 +162,12 @@ int main(int argc, char *argv[])
     ///
     UserInterface::manager().Terminate();
 
+    ///
+    /// MIXER TERMINATE
+    ///
+    while (Mixer::manager().busy())
+        Mixer::manager().update();
+
     ///
     /// RENDERING TERMINATE
     ///