Don't tick timer if in time trial countdown

In 2.2 and previous, the game would call resetgameclock() every frame
for the last 30 frames of the time trial countdown in order to make sure
it gets reset. This was in a render function, and didn't get brought out
in 2.3, so 2.3 resets the game clock *while rendering*, which is kinda
bad and is an oversight on my part for not noticing.

Instead of doing that, just add a conditional to the timer so that it
won't tick during the time trial countdown. This fixes #699 even further
by making it so the time trial par can't even be lost during the
countdown, because the timer won't tick up - so you can never get a sad
squeak to play by pausing the game or unfocus-pausing it during the
countdown.

desktop_version/src/Game.cpp

@@ -5683,6 +5683,11 @@ std::string Game::unrescued(void)
 
 void Game::gameclock(void)
 {
+    if (timetrialcountdown > 0)
+    {
+        return;
+    }
+
     frames++;
     if (frames >= 30)
     {