Skip game state update when nothing has changed

Don't update the game state and screen when less than one tick has
passed since last update.

Thanks to Sebastien Chevalier (ptitSeb).

AUTHORS.md

@@ -2,6 +2,7 @@
 * Simen Heggestøyl (simenheg@gmail.com)
 * Gwilym Kuiper
 * Patrick Bauge Skevik (patrisk@student.matnat.uio.no)
+* Sebastien Chevalier (sebastien.chev@gmail.com)
 
 ## Testing
 * Anders Heggestøyl (anders.heggestoyl@gmail.com)

src/zatackax.c

@@ -688,11 +688,16 @@ int logicGame(void)
     Uint32 delta = timenow - prevtime;
     prevtime = timenow;
 
-    if (olvl >= O_DEBUG)
+    if (olvl >= O_DEBUG) {
         fprintf(stderr, "delta: %d    prevtime: %d\n", delta, prevtime);
+    }
 
-    if (delta > 35)
+    if (delta > 35) {
         delta = 35;
+    }
+    else if (delta == 0) {
+        return 0;
+    }
 
     for (i = 0; i < MAX_PLAYERS; ++i) {