Fix deltaframe tower BG flicker when exiting menu in H/V warp room

To fix this annoying flicker (which, btw, took me WAY too long to do), I
had to introduce yet another kludge variable to signal that the
horizontal/vertical warp background should be re-initialized on the
pause screen.

I think I could technically keep the 'graphics.backgrounddrawn = false;'
in maplogic() and remove the 'graphics.backgrounddrawn = false;' in
Game::returntopausemenu(), but I'm keeping that other one around because
it doesn't hurt and just as a general precaution and safety measure.

desktop_version/src/Logic.cpp

@@ -79,6 +79,16 @@ void maplogic()
     graphics.updatetextboxes();
     graphics.updatetitlecolours();
 
+    if (game.shouldreturntopausemenu)
+    {
+        game.shouldreturntopausemenu = false;
+        graphics.backgrounddrawn = false;
+        if (map.background == 3 || map.background || 4)
+        {
+            graphics.updatebackground(map.background);
+        }
+    }
+
     graphics.crewframedelay--;
     if (graphics.crewframedelay <= 0)
     {