Reverse menu animation direction in Flip Mode

In normal mode, the room name is at the bottom of the screen. When you
bring up the map screen, it appears as if the room name is moving up
from the bottom of the screen, and the map screen is "pushing" it up.
The effect is pretty seamless, and when I first played the game (back in
2014), I thought it was pretty cool.

However, in Flip Mode, the room name is at the top of the screen. So one
would expect the menu animation to come from above the screen. Well, no,
it still goes from the bottom of screen; ruining the effect because it
seems like there are two room names on the screen, when there ought to
be only one.

To be fair, I only noticed this while fixing another bug now, but it's
one of those things you can't unsee (I have cursed you with knowledge!);
not to mention that I probably only didn't notice this because I don't
play in Flip Mode that often (and I'd wager almost no one does; Flip
Mode previous to 2.3 seems to have been really untested, like I said
in #165). It feels like a bit of an oversight that the direction of the
animation is the same direction as in unflipped mode. So I'm fixing
this.

desktop_version/src/Graphics.cpp

@@ -2829,7 +2829,7 @@ void Graphics::menuoffrender(void)
 		BlitSurfaceStandard(tempbufferFlipped, NULL, backBuffer, NULL);
 		SDL_FreeSurface(tempbufferFlipped);
 		SDL_Rect offsetRect;
-		setRect (offsetRect, 0, usethisoffset, backBuffer->w ,backBuffer->h);
+		setRect (offsetRect, 0, -usethisoffset, backBuffer->w ,backBuffer->h);
 		SDL_Surface* temp = FlipSurfaceVerticle(menubuffer);
 		BlitSurfaceStandard(temp,NULL,backBuffer,&offsetRect);
 		SDL_FreeSurface(temp);