Fix Flip Mode persisting in in-game options menu

Now graphics.flipmode is turned off when going into the menu, and turned
back on if necessary when exiting.

desktop_version/src/Game.cpp

@@ -7764,4 +7764,5 @@ void Game::returntopausemenu()
     map.kludge_to_bg();
     map.tdrawback = true;
     game.mapheld = true;
+    graphics.flipmode = graphics.setflipmode;
 }