Fix 1-frame background glitch when returning from in-game options

The background would change for 1 frame before sending you back to the
pause menu or editor settings. The map.nexttowercolour() call needs to
be deferred until the end of the frame.

desktop_version/src/Game.cpp

@@ -6632,6 +6632,11 @@ static void returntoedsettings(void)
 }
 #endif
 
+static void nextbgcolor(void)
+{
+    map.nexttowercolour();
+}
+
 void Game::returntoingame(void)
 {
     ingame_titlemode = false;
@@ -6655,6 +6660,7 @@ void Game::returntoingame(void)
             obj.flags[73] = true;
         }
     }
+    DEFER_CALLBACK(nextbgcolor);
 }
 
 void Game::unlockAchievement(const char *name) {

desktop_version/src/Input.cpp

@@ -1638,10 +1638,9 @@ void titleinput(void)
                 else
                 {
                     game.returnmenu();
+                    map.nexttowercolour();
                 }
             }
-
-            map.nexttowercolour();
         }
 
         if(game.menustart)