[skip ci] handle missing timers better

ml-agents/tests/yamato/training_int_tests.py

         timer_data = json.load(f)
 
     gauges = timer_data.get("gauges", {})
-    rewards = gauges.get("Override_3DBall.CumulativeReward")
+    rewards = gauges.get("Override_3DBall.CumulativeReward", {})
     max_reward = rewards.get("max")
     if max_reward is None:
         print(