Make slowdown only apply in GAMEMODE/MAPMODE/TELEPORTERMODE

As much as it looks cool to have a slowly-scrolling background on the
title screen, it's quite annoying that slowmode applying on the title
screen mean that your keypresses are less responsive.

desktop_version/src/main.cpp

@@ -330,10 +330,14 @@ int main(int argc, char *argv[])
         {
             timesteplimit = 24;
         }
-        else
+        else if (game.gamestate == GAMEMODE || game.gamestate == MAPMODE || game.gamestate == TELEPORTERMODE)
         {
             timesteplimit = game.gameframerate;
         }
+        else
+        {
+            timesteplimit = 34;
+        }
 
         while (accumulator >= timesteplimit)
         {