Call nexttowercolour() when exiting to menu

This fixes a bug where you could get mismatched text and background
colors on the menu screen by being in the Tower and exiting at a certain
time. The background when mismatched will always be red, which seems to
have something to do with the fact that when you enter the Tower the
game always sets the background to be red. I could get a quick repro
setup going by starting in the checkpoint in Teleporter Divot, then
quickly entering the Tower, exiting, then re-entering, then pressing Esc
and quitting - all done very quickly.

The important thing about this mismatch is that it's only temporary, and
will be corrected when you press ACTION and the color of the text and
background in the menu both change at the same time, which is what
map.nexttowercolour() does. So all I do is simply call that function
when exiting to the menu, and it will fix the color mismatch.

desktop_version/src/Input.cpp

@@ -2336,6 +2336,7 @@ void mapinput(KeyPoll& key, Graphics& dwgfx, Game& game, mapclass& map,
                 if(dwgfx.setflipmode) dwgfx.flipmode = true;
                 dwgfx.fademode = 2;
                 music.fadeout();
+                map.nexttowercolour();
             }
         }