De-duplicate zeroing the game clock

For some reason, resetgameclock() is only ever used in gamerender(), and
everywhere else just zeroes the clock manually. This is weird to me, so
I've made it so everywhere that zeroes the clock uses the
resetgameclock() function to do so.

desktop_version/src/Game.cpp

@@ -214,10 +214,7 @@ void Game::init(void)
 
     deathcounts = 0;
     gameoverdelay = 0;
-    frames = 0;
-    seconds = 0;
-    minutes = 0;
-    hours = 0;
+    resetgameclock();
     gamesaved = false;
     gamesavefailed = false;
     savetime = "00:00";