Rename tempBuffer to menuoffbuffer

In general, "temp" is a bad name because it could mean anything. In this
case the buffer isn't really temporary and it's only used for drawing
the menu with a certain offset, so I made it use a better name. But also
because I'm going to be adding temporary buffers so I don't want the
names to be confused.

desktop_version/src/Input.cpp

@@ -3074,7 +3074,7 @@ static void mapmenuactionpress(const bool version2_2)
 
         //Kill contents of offset render buffer, since we do that for some reason.
         //This fixes an apparent frame flicker.
-        ClearSurface(graphics.tempBuffer);
+        ClearSurface(graphics.menuoffbuffer);
         graphics.fademode = FADE_START_FADEOUT;
         music.fadeout();
         map.nexttowercolour();